refactor(cache): remove dead Cache._native_cache runtime path

[devin-ai-integration]

Summary

Cache._native_cache has had no assigner since #43601, and the V2 cache (litellm/_v2/cache plus python-bridge/src/cache/native/v2.rs and NativeCacheHandle) replaced it. Everything reachable only through that slot is removed

Python: the _native_cache attribute and its branches in get_cache, async_get_cache, add_cache, async_add_cache and async_add_cache_pipeline, the _native_response, _native_request and _stamp_semantic_similarity helpers, litellm/rust_bridge/response_cache.py, and the _ResponseCacheRuntime stub in _native.pyi. Python cache reads and writes keep going through self.cache / dynamic_cache_object exactly as before

Rust (python-bridge/src/cache/): runtime.rs (_ResponseCacheRuntime, CacheBinding), future.rs, python/callback.rs, and native/{activation,backend,config,embedder,facade,identity,request,semantic}.rs, plus the _ResponseCacheRuntime registration in lib.rs. native/v2.rs used super::request::now(), so it now has its own now(). selection.rs, python/{host,service}.rs and native/v2.rs stay

Deps dropped from python-bridge only: litellm-cache-{azure-blob,s3,gcs,disk,redis-semantic,qdrant-semantic,valkey-semantic}, qdrant-client, url, and the sha2 dev-dependency. The crates themselves and their tests are unchanged

Tests: tests/test_litellm_rust/cache/test_{redis,s3,gcs,azure_blob,disk,redis_semantic,valkey_semantic,qdrant_semantic,facade,rollout}.py, support/s3_stub.py with its fixture, and the activate_native / native_runtime / CacheTestResolver helpers in support/cache.py

Verified locally: cargo clippy -p litellm-python-bridge --all-targets -- -D warnings clean, tests/unit/caching 588 passed, tests/test_litellm_rust/cache + tests/unit/rust_bridge 1286 passed with LITELLM_RUST=1 on a rebuilt extension, make check PASS

Link to Devin session: https://app.devin.ai/sessions/2ace2cec0f4e485f8cad590dbf4a1473
Open in Devin Desktop: https://app.devin.ai/desktop/session/2ace2cec0f4e485f8cad590dbf4a1473?variant=devin
Requested by: @yujonglee-berri

[devin-ai-integration]

I'll fix CI failures and address comments from users with write access. I'll skip comments containing "(aside)".

• Disable automatic comment, CI, and merge conflict monitoring

[greptile-apps]

Confidence Score: 5/5

[High risk] Removes large native cache backend implementation from Rust bridge.

The PR appears safe to merge.

Summary

The PR removes the unused Cache._native_cache runtime path and its Python and Rust bindings, dependencies, and tests. The V2 native cache handle and the existing Python cache fallback remain.

_{Reviews (1) · Last reviewed commit: "refactor(cache): remove dead Cache._nati..."}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[codspeed]

Merging this PR will not alter performance

✅ 31 untouched benchmarks

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_{Comparing litellm_remove_native_cache_runtime (d36aba7) with main (a983b2a)}