feat(laravel): go-to-definition and find-references for config keys and env variables

[MingJen]

Summary

• Config key navigation: Ctrl-clicking config('app.name'),
  Config::get('app.name'), or Config::set('app.name') now jumps to
  the matching key declaration in config/app.php. Nested paths (e.g.
  config('api.keys.secret')) resolve into subdirectory config files.
• Find References on config keys: from any usage site or declaration,
  "Find All References" lists every call site across the project plus the
  declaration in config/*.php. Uses pre-built SymbolKind::LaravelStringKey
  spans — no per-file re-parse.
• Env variable navigation: Ctrl-clicking env('APP_KEY') jumps to the
  corresponding line in .env.
• Generic PHP AST walker: extracts walk_all_php_expressions and
  extract_string_literal into laravel/helpers.rs to avoid boilerplate
  duplication in future Laravel-specific navigations.

How it works

Config key usages (config(), Config::get, Config::set) are indexed as
SymbolKind::LaravelStringKey during workspace scan. Cross-file reference
search iterates these pre-built spans identically to the existing
find_member_references pattern — O(symbols), not O(files × parse-cost).

Declaration lookup parses only the target config/*.php file on demand;
that file set is small (typically < 20) and each parse is cheap.

Env variable resolution is single-file only: it parses the current file to
locate the cursor's env('KEY') call, then does a text search in .env.

Test plan

• cargo test — 395 passed
• cargo clippy — clean
• cargo fmt --check — clean
• php -l example.php / assertions — pass
• Integration tests: 7 new test cases covering config usage→declaration,
  nested keys, find-references from usage and declaration sites
• integration test for env() go-to-definition

[AJenbo]

Nice addition I clean up some minor things and added triggers for Config::string, Config::boolean etc.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 68.46473% with 228 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.32%. Comparing base (4724051) to head (1d7c9b0).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/virtual_members/laravel/helpers.rs	24.78%	179 Missing ⚠️
src/virtual_members/laravel/config_keys.rs	86.90%	36 Missing ⚠️
src/symbol_map/extraction.rs	95.08%	3 Missing ⚠️
src/definition/resolve.rs	83.33%	2 Missing ⚠️
src/virtual_members/laravel/env_vars.rs	97.53%	2 Missing ⚠️
src/highlight/mod.rs	0.00%	1 Missing ⚠️
src/hover/mod.rs	0.00%	1 Missing ⚠️
src/references/mod.rs	93.75%	1 Missing ⚠️
src/rename/mod.rs	0.00%	1 Missing ⚠️
src/semantic_tokens.rs	0.00%	1 Missing ⚠️
... and 1 more

❌ Your patch status has failed because the patch coverage (68.46%) is below the target coverage (80.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #93      +/-   ##
==========================================
- Coverage   86.42%   86.32%   -0.10%     
==========================================
  Files         162      164       +2     
  Lines      102869   103617     +748     
==========================================
+ Hits        88901    89445     +544     
- Misses      13968    14172     +204     

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