feat(compiler): add KSP2 support with compatibility and performance validation

[zhi1ong]

Summary / 变更说明

Add a standalone KSP2 compiler so Android modules can generate ARouter route/provider registries, injection helpers, interceptor registries and route documentation without running ARouter through KAPT. Keep the existing APT/KAPT compiler and runtime contracts intact; mixed applications can use different backends in separate modules, including precompiled KAPT parents.

The implementation includes deferred symbol handling, explicit diagnostics for unsupported Kotlin fields, inherited/generic field mapping, and incremental deletion/ancestor-change coverage. Round-scoped analysis and narrower aggregate dependencies reduce redundant compiler work while preserving generated output.

Related issue / 关联 Issue

Related to #959. The new artifact is a local development snapshot; publishing a release is outside this PR.

Compatibility / 兼容性

• KSP 2.3.12, Kotlin 2.3.20 and JDK 17; the standalone producer uses Gradle 9.5 and emits Java 8 bytecode.
• Consumer matrix: AGP 8.12.0 / Gradle 8.13 / API 34; AGP 9.0.0 / Gradle 9.1.0 / API 34; AGP 9.3.2 / Gradle 9.5 / API 21 and 34. The AGP 9.3 row is empirical compatibility coverage beyond Kotlin 2.3.20's officially documented full-support range.
• No Android runtime/public API change. Generated names and registration contracts remain compatible with the existing plugin/manual registration paths.
• One ARouter backend per module. Kotlin injection supports accessible mutable @JvmField and lateinit fields; ordinary properties and other unsupported cases receive documented diagnostics.

Validation / 验证

• Added focused regressions: 35 real KSP/JVM tests pass on the final implementation.
• Final optimized sources pass the AGP 8.12/API 34 consumer verifier, Debug and Release/R8 emulator tests, and incremental route deletion, unannotated-ancestor and inherited-field changes.
• All four consumer matrix rows passed in GitHub Actions on final head c8e7b528b6ea53f4621670b173ff4479214637e3, including the analysis optimization, Debug/Release-R8 device tests and incremental mutation checks.
• Existing APT tests and the legacy Kotlin 1.4.10/JDK 8 KAPT compilation chain passed during development. The complete legacy build, four Gradle plugin compatibility rows, six device test rows, IDE navigation tests, wrapper validation, CodeQL and CLA also passed in PR CI.
• Controlled KAPT/KSP benchmark: 140 measured samples plus warmups across seven scenarios. Optimization comparison: 100 measured samples plus warmups across five scenarios, with all 134 generated Java files byte-identical before/after. Improvements and remaining tradeoffs are documented in BENCHMARK.md and OPTIMIZATION.md; no universal speedup is claimed.
• No generated consumer sources, build reports, credentials or unrelated formatting are included. The standalone Gradle wrapper JAR is intentionally tracked.
• The pull request targets develop.
• All commit authors have completed the required CLA check (license/cla passed on this PR).

Final CI: all 20 checks passed. Build run: https://github.com/alibaba/ARouter/actions/runs/34693662788