Report the stanc flags make/local added in stan_build_info()

[jgabry]

Submission Checklist

• Run unit tests
• Declare copyright holder and agree to license (see below)

Summary

This PR and the summary below were assisted by AI. I have reviewed all code and doc.

---

stan_build_info() now includes stanc_options_from_make under
configuration: the STANCFLAGS that make/local added to the stanc call,
minus any the call's own stanc_options overrode. The build record already
held it; #1278 left it out of the public result and Codex's review suggested
adding it. The case is the same as for include_paths: make/local can
change after a build, so the file alone doesn't say which flags the build
saw.

• R/build_record.R: the field in the result and a printer line after
  stanc_options; roxygen bullet, and the "leaves out" paragraph no longer
  names it.
• dev-notes/compilation-state.md §8: withheld sentence and diagnosis rule
  updated, example shape gains the field; contract regenerated.
• tests/testthat/test-build-info.R: the field is expected in the public
  shape and read back as recorded.

The second commit makes the function visible and tidies its printer:

• vignettes/cmdstanr-internals.Rmd: the build record section reads the
  record back with $build_info() and points at stan_build_info(). The
  example now copies bernoulli into tempdir() under its own name, so the
  paths and the record file read as bernoulli rather than a random
  tempfile name, and the record listing is narrowed to that model.
• print.stan_build_info(): include_paths prints "none" when empty like
  the other option lines, and the status lines for a missing, unreadable,
  mismatched or wrong-format record are under 80 characters and say what
  happened and what to do.
• One snapshot test covers the printed form of every record state, in place
  of the fragment checks.

Copyright and Licensing

Please list the copyright holder for the work you are submitting
(this will be you or your assignee, such as a university or company):
Jonah Gabry

By submitting this pull request, the copyright holder is agreeing to
license the submitted work under the following licenses:

• Code: BSD 3-clause (https://opensource.org/licenses/BSD-3-Clause)
• Documentation: CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)

[codecov-commenter]

Codecov Report

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Additional details and impacted files

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