template: preserve replacement config for nested substitutions

[WyRainBow]

Summary

Preserve interpolation config when recursively substituting the rest portion of braced expressions in DefaultReplacementAppliedFunc.

Before this change, the recursive call used SubstituteWith(rest, mapping, pattern), which dropped caller-provided options such as custom ReplacementFunc and WithoutLogging. This caused mixed expressions like ${FILE:-...} ${ENTRY_ID} to incorrectly process ${ENTRY_ID} with default behavior.

What changed

• Pass the current config context to nested substitution by using SubstituteWithOptions with:
  • WithPattern(cfg.pattern)
  • WithReplacementFunction(cfg.replacementFunc) when set
  • WithSubstitutionFunction(cfg.substituteFunc) when set
  • WithoutLogging when logging is disabled

Verification

• go test ./template -count=1
• go test ./... -count=1

Fixes #856