fix(compiler): surface template warnings and StringSliceMap YAML errors

[ecrupper]

We weren't surfacing warnings from template files.

We also weren't wrapping the YAML error for StringSliceMap which made any error related to that type incredibly vague.

[codecov]

Codecov Report

Attention: Patch coverage is 93.84615% with 4 lines in your changes missing coverage. Please review.

Project coverage is 56.59%. Comparing base (1c3c159) to head (485ebc3).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
compiler/native/expand.go	84.00%	4 Missing ⚠️

❌ Your project status has failed because the head coverage (56.59%) is below the target coverage (90.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1251      +/-   ##
==========================================
+ Coverage   56.55%   56.59%   +0.03%     
==========================================
  Files         629      629              
  Lines       35619    35645      +26     
==========================================
+ Hits        20146    20172      +26     
  Misses      14792    14792              
  Partials      681      681              

Files with missing lines	Coverage Δ
compiler/native/compile.go	70.31% <100.00%> (+0.95%)	⬆️
compiler/native/parse.go	85.12% <100.00%> (ø)
compiler/template/native/render.go	88.00% <100.00%> (ø)
compiler/template/starlark/render.go	46.58% <100.00%> (ø)
compiler/types/raw/map.go	77.88% <100.00%> (ø)
internal/yaml.go	82.14% <100.00%> (+0.66%)	⬆️
compiler/native/expand.go	68.54% <84.00%> (+0.85%)	⬆️