Skip rediscovery for unchanged AST

[thejchap]

Context

Discovery was keyed directly off source text, so trivia-only edits still forced test rediscovery even when the parsed AST did not change.

Changes

• Add a tracked parsed-AST layer before file discovery.
• Compare parsed AST bodies so unchanged ASTs can backdate downstream discovery work.
• Add a regression test covering comment-only edits versus real AST changes.
• Update README and docs index examples to import describe, Depends, fixture, test, and expect directly instead of using t.* qualification.

Test plan

• cargo test -p tryke_discovery
• cargo clippy --workspace --all-targets --all-features -- -D warnings
• cargo nextest run --workspace --all-features
• uv run cargo run -- test --reporter llm
• uvx prek run -a

[Copilot]

Pull request overview

This PR adds an incremental parsed-AST layer to tryke_discovery so discovery can be skipped when source edits do not change the parsed AST, and updates public documentation examples to use direct tryke imports.

Changes:

• Introduces ParsedAst and parse_file as a Salsa-tracked parsing layer before file discovery.
• Refactors discovery to consume parsed ASTs and adds a regression test for unchanged-AST edits.
• Updates README and docs examples from t.* usage to direct imports.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
crates/tryke_discovery/src/db.rs	Adds ParsedAst, tracked parsing, and test-only discovery execution counting.
crates/tryke_discovery/src/lib.rs	Refactors discovery from source parsing to AST-based discovery.
crates/tryke_discovery/src/discoverer.rs	Adds regression coverage for unchanged AST rediscovery behavior.
README.md	Updates example imports and call sites to direct tryke symbols.
docs/index.md	Mirrors README example import and call-site updates.

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