feat(memory): add RedisMemoryService

[volkthienpreecha]

Link to Issue or Description of Change

1. Link to an existing issue (if applicable):

• Related: Add support for additional Memory Bank services: DatabaseMemoryService/RedisMemoryService #2524

Problem:

ADK does not currently have a Redis-backed memory service. That means developers who want durable, self-hosted agent memory need to either use an existing hosted backend or keep memory in process with InMemoryMemoryService.

Solution:

I added RedisMemoryService as a focused implementation of the existing BaseMemoryService contract.

This PR adds Redis storage for memory events, lazy export from google.adk.memory, optional dependency support through google-adk[redis], and service registry support for redis:// and rediss:// memory service URIs.

Expected behavior:

After this change, developers can use Redis as a persistent memory backend. Sessions and events can be added to memory, searched by keyword, and scoped by app_name and user_id, while keeping behavior aligned with the existing InMemoryMemoryService.

Testing Plan

Unit Tests:

• I have added or updated unit tests for my change.
• All unit tests pass locally.

I added unit coverage for RedisMemoryService across session ingest, explicit event ingest, event appends, event deduping, session replacement, user scoping, case-insensitive search, empty sessions, and client cleanup.

I also added service registry tests for redis:// and rediss:// memory service URIs.

Passed locally:

PYTHONPATH=src python -m pytest \
  tests/unittests/memory/test_in_memory_memory_service.py \
  tests/unittests/memory/test_redis_memory_service.py \
  tests/unittests/cli/test_service_registry.py -q

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