Re-introduce conda_resolve_check.py (release-time channel-drift re-solve gate), wired + validated #755

Context

eng/scripts/conda_resolve_check.py (+ tests/test_032_conda_resolve_check.py) is a release-time dependency re-solve gate: it stages the consolidated conda tree as a local channel and re-runs conda create --dry-run for mssql-python=<version> against the live upstream channels per subdir, so channel drift (a dependency yanked or repinned between build and release) blocks the publish instead of breaking a user's conda install.

It was built and unit-tested but never wired into any pipeline — no OneBranch step invokes it, and the ValidateConda job has no conda/mamba to run it. Its docstring claimed it "blocks the publish," but in practice it gated nothing. It was therefore removed from PR #720 (commit 2439cde4) rather than shipping unwired dead code (an unwired script draws a "why isn't this called?" review comment regardless of docstring wording, and an untested pipeline gate would be worse than none).

Task — re-introduce it together with the wiring that makes it real

• Add a step to the release pipeline's ValidateConda job (OneBranchPipelines/steps/conda-release-step.yml) that runs conda_resolve_check.py --conda <exe> against the downloaded consolidated conda tree.
• Provision a conda/mamba solver in that job (an approved base image / internal feed — never a raw download in the Official publish pipeline, per the script's own note).
• Validate with a real release-pipeline run (or a NonOfficial dry-run that actually reaches the re-solve) before relying on it as a gate.
• Restore tests/test_032_conda_resolve_check.py and its conda-audit.yml path-filter + pytest references.

Recover the removed code with git show 2439cde4^:eng/scripts/conda_resolve_check.py (and the matching test) from microsoft/mssql-python.