feat(lint): add --fix option to auto-remove unused locals

[julienduchesne]

Summary

• Adds a --fix flag to rtk lint and the standalone jrsonnet-lint binary
• For the unused_locals check, the fix automatically removes the offending local statement from the source file
• Fix ranges are computed in the linter and attached to each Diagnostic via a new Fix struct
• A new apply_fixes public function in jrsonnet-lint applies all fixes to a source string (in reverse offset order to preserve positions)

How it works

• Single-bind local statements (local x = 1;): the entire statement is removed, including surrounding whitespace and trailing newline
• Object locals (local x = 1, inside {}): the member is removed, including surrounding whitespace and the trailing comma
• Multi-bind statements (local x = 1, y = 2;): no auto-fix (would require partial AST surgery); these are still reported as diagnostics
• When --fix is used, any diagnostics without a fix are still reported and cause a non-zero exit

Test plan

• cargo test -p jrsonnet-lint — 30 tests pass (4 new tests for apply_fixes)
• make test — full suite passes
• Manual: rtk lint --fix <dir> rewrites files in place
• Manual: jrsonnet-lint --fix <file> rewrites file in place
• Manual: jrsonnet-lint --fix - (stdin) warns and reports diagnostics normally

🤖 Generated with Claude Code

[github-actions]

Benchmark Results

Benchmark	Test	vs tk	vs base
Diff	cluster_scoped	48.14x faster	equal
Diff	configmap_unchanged	29.8x faster	equal
Diff	deployment_nested_changes	29.36x faster	equal
Env List	Single Inline Directory (--json)	47.08x faster	equal
Env List	Single Inline File (--json)	47.33x faster	equal
Env List	All Environments (--json)	86.16x faster	equal
Eval	Single Static Environment	15.14x faster	equal
Eval	Inline Environment File	22.91x faster	equal
Eval	Eval Expression - Deeply Nested Path	14.98x faster	equal
Export (Full)	Single Static Environment	5.51x faster	equal
Export (Full)	Single Inline Environment	14.21x faster	equal
Export (Full)	All Environments	12.06x faster	equal
Export (Replace)	Single Static Environment	5.17x faster	equal
Export (Replace)	Single Inline Environment	14.65x faster	equal
Export (Replace)	All Environments	19.63x faster	equal
Tool Importers Count	Single Lib Directory (Non-Recursive)	2.13x faster	equal
Tool Importers Count	Single Lib Directory (Recursive)	2.12x faster	equal
Tool Importers Count	Entire Lib Directory (Non-Recursive)	1.43x faster	equal
Tool Importers Count	Entire Lib Directory (Recursive)	1.07x faster	equal
Tool Importers	Global Lib File	2.26x faster	equal
Tool Importers	Single Env-Specific Lib File	1.68x faster	equal
Tool Importers	All Env-Specific Lib Files	6.77x faster	equal
Tool Importers	All Lib Files	7.02x faster	equal
Tool Importers	All Jsonnet Files	11.3x faster	equal
Tool Imports	Single Static Environment	3.44x faster	equal
Tool Imports	Single Inline Environment File	3.38x faster	equal

Full results available in workflow artifacts.

Benchmark run on commit 5c942dc3efb0a1f03f10529a08a52a900b99d137