fix(preprocess): optimize file patching and fix edge-case bugs

[nghiphaam]

Speeds up spicetify apply and cleans up a few issues in preprocess and utils:

• Cache compiled regexes and move static []Patch slices to package level.
• Use Find*SubmatchIndex in Replace* / FindFirstMatch / FindLastMatch to avoid matching twice and stop after the first match in ReplaceOnce.
• Use strings.NewReplacer for cssTranslationMap on CSS files (same as JS) and combine literal hex color patches.
• Parallelize file patching in Start and StartCSS using filepath.WalkDir.
• Fix potential nil dereference in StartCSS, duplicate Spicetify.URI patch, missing bounds check in SeekToCloseParen, and defer inside loops in Unzip/Copy.
• Skip writing unchanged files in ModifyFile.

Note: also removed --spice-card-elevated from colorPatches since it used the exact same #(242424|1f1f1f)\b regex as --spice-main-elevated above it and was unreachable.

Summary by CodeRabbit

• Performance
  • Preprocessing and CSS color conversion now run concurrently, which can speed up builds.
• Bug Fixes
  • CSS replacements are applied consistently, and XPUI stylesheets retain the legacy fixed-width grid rule.
  • Improved handling of logging and vendor integrations when processing supported application files.
  • File and archive operations now handle unchanged content and extraction errors more reliably.

[coderabbitai]

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Reviewing files that changed from the base of the PR and between a60d020 and 2227d71.

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⚙️ Run configuration

• Configuration used: Repository: spicetify/cli/.coderabbit.yaml
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📥 Commits

Reviewing files that changed from the base of the PR and between 1684023 and a60d020.

📒 Files selected for processing: 2

• src/preprocess/preprocess.go
• src/utils/utils.go

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📝 Walkthrough

The changes update utility regex and file operations, and revise preprocessing to discover and process files concurrently. Preprocessing also uses precomputed CSS replacements and shared patch definitions, with checks for context-menu and vendor URI matches.

Changes: Preprocessing and Utilities

Layer / File(s)	Summary
Regex matching and scanning helpers src/utils/utils.go	Compiled regexes are cached. Replacement and matching helpers use match indices, and parenthesis scanning is bounded by the content length.
Archive and file operations src/utils/utils.go	Archive entries are opened during extraction and closed after copying. Copy delegates to CopyFile. ModifyFile reports errors through PrintError, skips unchanged writes, and writes changed content with mode 0644.
Concurrent file preprocessing src/preprocess/preprocess.go	Start and StartCSS discover files with WalkDir and process them concurrently with CPU-count limits. CSS-map replacers are precomputed, and color conversion patches are shared.
Preprocessing patch rules and safeguards src/preprocess/preprocess.go	Logging, RTL, GraphQL, XPUI, and vendor patch definitions move to package scope. Context-menu discovery checks for a useRef match, and vendor URI export insertion checks for a URI body.

Priority: ⬇️ Low

Estimated code review effort: 4 (Complex) | ~45 minutes

Change: Bug fix

Sequence Diagram(s)

sequenceDiagram
  participant Start
  participant WalkDir
  participant Workers as Worker goroutines
  participant Progress as Progress bar
  Start->>WalkDir: Discover files
  WalkDir-->>Start: Return file entries
  Start->>Workers: Dispatch file processing
  Workers->>Progress: Increment progress under lock

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Suggested reviewers: rxri

Merge Risk: ⚪ Minimal · up to a60d0

The inspected preprocessing changes preserve the relevant replacement behavior. No actionable issue remains from this review; the PR is mergeable after normal checks.

Pre-merge checks: 4 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 30.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 30 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 4 passed

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title accurately summarizes the pull request. It identifies both the file-patching optimizations and the edge-case fixes described in the changes.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

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