feat(router): add lmdeploy router

[caikun-pjlab]

Summary

This PR integrates the Rust-based lmdeploy-router into the main LMDeploy repository, providing unified development, testing, packaging, documentation, and release management.

Key Changes

• Migrated the complete Rust router implementation to lmdeploy/router, including source code, benchmark suite, Python launcher, wheel packaging configuration, and tests.
• Replaced the legacy Python proxy with lmdeploy-router; lmdeploy serve proxy now remains as a compatibility entry point that launches the Rust router.
• Kept lmdeploy-router as an independent Python distribution while colocating its source in the LMDeploy repository. The wheel provides the Python launcher, lmdeploy_router_rs extension, and standalone router binary.
• Added unified router CI for:
  • cargo fmt
  • cargo clippy
  • Rust tests
  • Python unit tests
  • mock-based Python integration tests
• Expanded router integration coverage for REST APIs, worker registration and removal, load-balancing policies, authentication, retries, circuit breaking, rate limiting, payload handling, and prefill-decode routing.
• Added real-engine e2e tests for regular serving, and PD disaggregation. PD disaggregation ci test is skipped now, because machine does not support RDMA.
• Updated the PR function-test workflow so existing lmdeploy serve api_server tests run through lmdeploy-router, ensuring REST traffic is exercised through the router in real CI environments.
• Added a PD disaggregation e2e stage for Qwen/Qwen3.5-35B-A3B, deploying separate Prefill and Decode instances and routing requests through lmdeploy-router.
• Integrated router construction into the main LMDeploy Docker image by default, with BUILD_ROUTER=0 available to skip Rust compilation when router support is not needed.
• Updated English and Chinese documentation with installation, routing-policy, dynamic registration, PD deployment, migration, and compatibility guidance.
• Added a manual router release workflow that builds wheel artifacts by default and only uploads to PyPI when explicitly enabled.

Compatibility

• The lmdeploy serve proxy command is preserved for compatibility.
• Legacy min_expected_latency and min_observed_latency routing values are accepted and mapped to cache_aware.
• The old Python proxy implementation and its internal import paths are removed; users should use lmdeploy-router or the compatibility CLI entry point.
• The router wheel remains independently versioned and is decoupled from the main LMDeploy wheel.

Testing

• Rust formatting, static analysis, and tests run in router CI.
• Python unit and mock integration tests run in router CI.
• Real-model PR function tests now exercise requests through lmdeploy-router.
• Docker image builds support both router-enabled and router-disabled modes.
• Documentation formatting, Python linting, YAML parsing, and workflow shell syntax have been validated.