Mattpollock feat/r client skip parsing

[wing328]

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Summary by cubic

Add an optional .parse flag to generated R client methods so callers can skip parsing and get raw response text. Default behavior stays the same.

• New Features

  • Added .parse (default TRUE) to R API methods that return data; when FALSE, methods return unparsed text.
  • Applied to both primitive and model return types.
  • Updated r/api.mustache and regenerated samples (echo_api and petstore across R, R-httr2, and R-httr2-wrapper).

• Migration

  • No breaking changes; existing calls continue to parse.
  • To get raw responses, pass .parse = FALSE.
  • Endpoints that return void do not include .parse.

^{Written for commit 2b702ca. Summary will update on new commits.}