perf(templates): cache parsed templates keyed by mtime

[KrisSimon]

Migrated from GitLab MR !179 (merged)
perf/cache-template-parse-160 → main
Originally created: 2026-03-19
Merged: 2026-03-22
Author: Kris Simon
Labels: next

Summary

• Every render/renderAndTrack call previously read the template file from disk and re-parsed it on every invocation — wasteful in tight render loops (e.g. TUI refreshing 10×/s)
• Added ParseCache actor inside AROTemplateService storing ParsedTemplate objects keyed by file path
• Embedded/registered templates are cached unconditionally (set-once semantics, never change)
• File-system templates are validated by mtime: re-parsed only when the file changes on disk; otherwise the cached ParsedTemplate is returned immediately
• Both render() and renderAndTrack() share the new loadAndParse() helper — cache is always warmed regardless of which path is taken

Closes #160

Test plan

• swift build passes cleanly
• All 1319 tests pass (swift test)
• 5 new TemplateParseCacheTests cover: first render caches, mtime invalidation, path-keying across multiple templates, registered template caching, renderAndTrack cache hit