perf: cache prefixed keys on TemplateResource initialization

[abtreece]

Summary

• Cache the result of util.AppendPrefix() on TemplateResource initialization to avoid repeated computation on every process() cycle
• Add prefixedKeys field to TemplateResource struct computed once during initialization
• Update backendFetcher to store and use pre-computed prefixed keys
• Change fetchValues() signature to use stored keys instead of parameter

Test plan

• Unit tests pass (go test ./...)
• Build succeeds (make build)
• Integration tests (requires backend services)

Fixes #445

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 83.33333% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 59.80%. Comparing base (ea56f0f) to head (5a06a59).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/template/processor.go	50.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #457      +/-   ##
==========================================
- Coverage   59.82%   59.80%   -0.02%     
==========================================
  Files          48       48              
  Lines        5244     5244              
==========================================
- Hits         3137     3136       -1     
- Misses       1901     1902       +1     
  Partials      206      206              

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[Copilot]

Pull request overview

This PR optimizes template processing by caching prefixed keys at initialization time rather than computing them repeatedly during each process cycle. This addresses performance issue #445 by eliminating redundant util.AppendPrefix() calls.

Changes:

• Add prefixedKeys field to TemplateResource struct, computed once during initialization
• Update backendFetcher to store and use pre-computed prefixed keys
• Remove keys parameter from fetchValues() method signature

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
pkg/template/resource.go	Add prefixedKeys field and compute it during initialization; pass to backend fetcher
pkg/template/processor.go	Replace repeated util.AppendPrefix() calls with cached prefixedKeys field
pkg/template/preflight.go	Use cached prefixedKeys instead of computing on-demand
pkg/template/backend_fetcher.go	Store prefixed keys and remove parameter from fetchValues()
pkg/template/backend_fetcher_test.go	Update test cases to provide PrefixedKeys in config

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[Copilot]

The field prefixedKeys should follow Go naming conventions and be exported as PrefixedKeys since it's being passed to other packages (e.g., in backendFetcherConfig). Alternatively, if it should remain unexported, the backendFetcherConfig.PrefixedKeys field should also be unexported.

[Copilot]

The field prefixedKeys is unexported but receives data from an exported field PrefixedKeys in the config struct. For consistency, either both should be exported or both should be unexported.