Add Tree Ring Memory provider

[TerminallyLazy]

Summary

Adds a local Tree Ring Memory provider to AMB.

The provider:

• uses the tree-ring Rust CLI via TREE_RING_BIN or PATH
• imports benchmark documents through Tree Ring's JSONL import path instead of argv, so larger documents do not hit command-line length limits
• maps AMB user_id to Tree Ring project for scoped recall
• retrieves through tree-ring recall --include-sensitive so personal-context benchmarks remain evaluable while Tree Ring still blocks secret-like imports
• registers the provider in the runtime registry and static catalog

I did not add benchmark leaderboard results in this PR; this only makes the provider runnable in the harness.

Validation

From this branch:

• python3 -m compileall src/memory_bench/memory/tree_ring.py src/memory_bench/memory/__init__.py
• uv run omb providers includes tree-ring
• generated catalog contains the tree-ring provider entry
• local smoke with TREE_RING_BIN=/Users/lazy/Projects/Tree_Ring_Memory/target/debug/tree-ring passed ingest + scoped recall
• git diff --check

Tree Ring binary used for the smoke was built from TerminallyLazy/Tree-Ring-Memory with:

• cargo build -p tree-ring-memory-cli