…on-datasource (apache#24006)

## Which issue does this PR close?

- Part of apache#23494. Precursor for apache#23497 / apache#23683 (`DataSource` /
`FileSource` proto hooks) and for apache#23752.

## Rationale for this change

The protobuf conversions for the file-scan leaf types —
`PartitionedFile`,
`FileGroup`, `FileRange` — live in `datafusion-proto` as `TryFromProto`
impls,
because that is historically the only crate that can name both sides
(the
DataFusion type and the prost message are both foreign to it, hence the
`TryFromProto` workaround trait in the first place).

That placement means any *other* crate that needs those conversions has
to
reimplement them. apache#23683 hits exactly this: a `FileSource` serializing
its own
scan config needs to encode file groups, so the first cut of that PR
grew a
private second copy of the `PartitionedFile` wire logic inside
`datafusion-datasource`, which can then drift from the central
serializer.
The same will be true of every source migrated under apache#23516–apache#23518.

Nothing about these conversions needs `datafusion-proto`: they are plain
data,
with `ScalarValue` / `Statistics` / `Schema` going through
`datafusion-proto-common`. They belong next to the types.

## What changes are included in this PR?

- New `datafusion_datasource::proto` module, behind a new `proto`
feature on
`datafusion-datasource` (off by default; `datafusion-proto` enables it):
  - `FileRange::try_to_proto` / `try_from_proto`
  - `PartitionedFile::try_to_proto` / `try_from_proto`
  - `FileGroup` <-> `protobuf::FileGroup`
- `datafusion-proto`'s `TryFromProto` impls for those types become
one-line
shims delegating to the new impls, so every existing caller keeps
working
  and the two sides cannot disagree.

### Why these are `TryFrom` and not `try_to_proto` hooks

`TryFromProto` exists because `datafusion-proto` owns neither side of
the
conversions it hosts: with both the DataFusion type and the prost
message
foreign to it, `impl TryFrom<protobuf::X> for X` is rejected by the
orphan
rule, so a local trait was the only way to say the same thing.

Moving a conversion into the crate that owns the DataFusion type removes
that
constraint, and `&T` is `#[fundamental]`, so both directions are
expressible
with the standard trait (checked, not assumed):

```rust
impl TryFrom<&protobuf::PartitionedFile> for PartitionedFile   // ok
impl TryFrom<&PartitionedFile> for protobuf::PartitionedFile   // ok
impl TryFrom<&[PartitionedFile]> for protobuf::FileGroup       // E0117
```

The last one is why `protobuf::FileGroup`'s *slice* conversion stays a
`TryFromProto` shim: `&[PartitionedFile]` is not a type this crate owns,
while
`&FileGroup` is. Callers inside DataFusion go through `FileGroup`.

So the rule this PR sets for the rest of apache#23494: **plain data uses
`TryFrom`;
anything needing an encode/decode context keeps the `try_to_proto(ctx)`
/
`try_from_proto(node, ctx)` hooks**, because the standard trait cannot
carry
that second argument. Usefully, none of the ~40
`TryFromProto`/`FromProto`
impls needs a context, and nothing that needs one was ever a
`TryFromProto`
impl — the two categories are already disjoint, so the shape now tells a
reader whether a conversion recurses.

### Why now

`FromProto` / `TryFromProto` were added in apache#21929, *after* the 54.0.0
release,
and 54.1.0 was cut before any of this landed — so they have never
shipped in a
release. Replacing them with the standard traits, and eventually
deleting them,
is a no-op for semver **today** and a major breaking change the moment
55.0.0
goes out. The same applies to the six inherent `try_to_proto` /
`try_from_proto`
methods this PR would otherwise have added: they are new, unreleased
API, so
choosing their final shape costs nothing right now.

The other reason to settle it here rather than in a follow-up: this is
the PR
that establishes the pattern for the data-source family (apache#23516-apache#23519
and
apache#23752 / apache#23781 are all queued behind it). Whichever shape merges first
is the
one they will copy.

Retiring the remaining ~34 impls is still its own follow-up. Two notes
for
whoever picks it up: the sink and format-option conversions can move
next to
their types the same way, but the ones for `datafusion-common`-owned
types
(`JoinType`, `NullEquality`, `TableReference`, `UnnestOptions`, ...)
cannot —
`datafusion-common` cannot depend on `datafusion-proto-models` (it is
underneath it via `datafusion-proto-common`). Their legal home is
`proto-models` itself, implementing on the local proto type, which is
already
how `proto-common` hosts the `ScalarValue` / `Statistics` conversions.

## Are these changes tested?

Yes.

- New unit tests in `datafusion_datasource::proto` covering the
`PartitionedFile` round trip (path, size, mtime, partition values,
range,
arrow schema, statistics), the `FileGroup` round trip, and the
invalid-path
  error.
- The existing `datafusion-proto` tests now exercise the delegating
shims, so
  they also pin the shims themselves.
- `datafusion-proto`, all features: 227 passed / 0 failed.
- `datafusion-datasource` with `proto`: 180 passed / 0 failed.
- Full workspace run: 10347 passed
(`cargo test --profile ci --workspace --lib --tests --features
avro,json,backtrace,extended_tests,recursive_protection,parquet_encryption`).
The only failures are 8 backtrace-symbolization tests in
`datafusion-common`,
a crate this PR does not touch and which sits below every crate it does;
they
  fail the same way on the base commit on macOS.
- `cargo fmt` and `ci/scripts/rust_clippy.sh` clean.

## Are there any user-facing changes?

The protobuf wire format is unchanged, and no existing API changes
shape.

Additive:

- New `proto` feature on `datafusion-datasource` (off by default).
- New `TryFrom` impls in both directions between `FileRange`,
  `PartitionedFile`, `FileGroup` and their protobuf messages, under that
feature. No new names are added to the crate's API surface: the trait is
  `core::convert::TryFrom`.

Note for reviewers: while writing the round-trip test I found that
`PartitionedFile` statistics do not round-trip cleanly on `main` — filed
as
apache#23998. This PR preserves that behavior exactly rather than changing
decode
semantics in a refactor; the test documents it.

---------

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>