perf(rust): pre-compute metadata and optimize WASM binary size

[codetiger]

Summary

• docs: Update datalogic-rs repository URL from cozylogic to GoPlasmatic org
• build: Optimize release profile for WASM binary size (opt-level = "z", codegen-units = 1) — reduces WASM binary from 2.59 MB to 1.97 MB (~24% smaller)
• perf: Pre-compute merged metadata at parse time and store in Arc for cheap cloning, use Cow<str> in resolve_string_from_context to avoid allocations, remove global OnceLock singleton in favor of reusing the evaluator's DataLogic engine, and use entry API with pre-allocated maps

Test plan

• All existing tests pass (cargo test)
• Benchmarked native performance: no meaningful regression (all changes within ±3% noise)
• WASM binary size verified: 2.59 MB → 1.97 MB (23.9% reduction)