perf(hir): cache type inference queries

[hongjr03]

Summary

• Registers type inference entry points as salsa queries on HirDb returning Arc-wrapped TyResult values.
• Keeps recursive inference internals on private implementation functions so existing typedef cycle handling remains unchanged.
• Moves IDE consumers to database query methods while leaving helper views such as members_of_ty as free functions.

Validation

• cargo build --workspace
• cargo test --workspace
• cargo fmt --all -- --check
• cargo clippy --workspace --all-targets -- -D warnings
• git diff --check

[github-actions]

Docs preview: https://vide.pascal-lab.net/preview/pr-284/