Add semantic analysis benchmarks and optimization documentation

- Add divan benchmarks for compiler semantic analysis phase
  (internal/compiler/benches/semantic_analysis.rs)
- Add custom allocator to track allocations in the benchmark.
- Add benches for individual phases of compilation and a proc-macro simulation mode.

- Document allocation hotspots and optimization strategies
  (docs/semantic-analysis-optimization.md)

Benchmarks cover:
- Lexing and parsing performance
- Full compilation with various stress scenarios
- Specific hotspots: many children, properties, exports,
  states, nested components, deep expressions, binding chains

The optimization doc identifies key issues:
- O(n²) export sorting
- Element duplication in inlining pass
- Incremental Vec growth patterns
- SmallVec sizing recommendations

Author: tilladam