perf: pre-allocate template slice in getTemplateResources

[abtreece]

Summary

• Pre-allocate template slice capacity in getTemplateResources() using the count from RecursiveFilesLookup
• Eliminates repeated slice growth allocations during template loading

Test plan

• All unit tests pass (go test ./...)
• Build succeeds (go build ./...)

Fixes #441

[Copilot]

Pull request overview

This PR optimizes memory allocation in the template loading process by pre-allocating the slice capacity based on the number of discovered template files, eliminating the need for multiple slice growth operations during appending.

Changes:

• Moved slice initialization to after template file discovery to leverage the known count for capacity pre-allocation

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 59.64%. Comparing base (cf11fa9) to head (a89de73).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #454      +/-   ##
==========================================
- Coverage   59.69%   59.64%   -0.06%     
==========================================
  Files          48       48              
  Lines        5223     5223              
==========================================
- Hits         3118     3115       -3     
- Misses       1901     1903       +2     
- Partials      204      205       +1     

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