Split oversized test modules

[yvette-carlisle]

Summary

• split memory policy integration tests into decision, precedence, threshold, and support modules
• split HTTP sharing and request validation tests into focused submodules
• split service acceptance suite support into config, provider, and runtime modules while preserving existing helper names

Validation

• RUSTC=/run/current-system/sw/bin/rustc cargo make fmt-rust
• RUSTC=/run/current-system/sw/bin/rustc cargo make check

Batch size: 18 files, 2068 insertions, 1996 deletions.