fix(IBA): keep nearest resample off the Highway path

[wingfiring]

Description

resample_hwy() ignores its interpolate argument and always bilerps, but resample_() routed nearest sampling to it whenever Highway was enabled, so ImageBufAlgo::resample(dst, src, false) returned filtered pixels instead of the source pixel the caller asked for. Measured against a 128x128 nearest resample of testsuite/common/grid.tif, 40.9% of pixels were wrong, with a maximum error of 0.608.

Latent today because enable_hwy defaults to 0, but it becomes a live behavior change as soon as Highway is turned on by default.

Also fixes an MSVC build failure in the same subsystem. The two hwy_*_perpixel_op_rgba_rgb_roi() lambdas derived a tag type with decltype(d), where d is captured from the enclosing function; MSVC yields a reference type there, and D::template Rebind cannot be named through a reference. Naming the tag directly drops the dependency on how decltype treats a captured entity, and says what the tag is rather than what it matches.

Tests

Case added: test_resample_hwy_nearest

Checklist:

• I have read the guidelines on contributions and code review procedures.
• I have read the Policy on AI Coding Assistants
  and if I used AI coding assistants, I have an Assisted-by: TOOL / MODEL
  line in the pull request description above.
• I have updated the documentation if my PR adds features or changes
  behavior.
• I am sure that this PR's changes are tested in the testsuite.
• I have run and passed the testsuite in CI before submitting the
  PR, by pushing the changes to my fork and seeing that the automated CI
  passed there. (Exceptions: If most tests pass and you can't figure out why
  the remaining ones fail, it's ok to submit the PR and ask for help. Or if
  any failures seem entirely unrelated to your change; sometimes things break
  on the GitHub runners.)
• My code follows the prevailing code style of this project and I
  fixed any problems reported by the clang-format CI test.
• If I added or modified a public C++ API call, I have also amended the
  corresponding Python bindings. If altering ImageBufAlgo functions, I also
  exposed the new functionality as oiiotool options.