chore(ci): bump Node 20 actions to Node 24 runtime

[zfarrell]

Bumps GitHub Actions still running on the deprecated Node 20 runtime to current Node 24-capable releases across CI and release workflows.

Bumps:

• actions/checkout: v4 -> v6.0.2
• actions/upload-artifact: v4 -> v7.0.1
• actions/download-artifact: v4 -> v8.0.1
• actions/setup-python: v5 -> v6.2.0
• astral-sh/setup-uv: v3 -> v8.1.0
• rust-lang/crates-io-auth-action: v1 -> v1.0.4
• ytanikin/pr-conventional-commits: 1.4.0 -> 1.5.2

Breaking changes to review:

• actions/checkout v4->v6: dropped Node20 for Node24; requires a runner supporting Node24. No input changes for this usage.
• actions/upload-artifact v4->v7: artifacts are now immutable (no overwrite/append). Matrix uses distinct names so no collision, but single-job re-runs cannot re-upload the same name without overwrite handling.
• actions/download-artifact v4->v8: must pair with upload-artifact v4+ (already the case); verify the release job's wheels-/ glob still resolves against the per-artifact subdir layout.
• actions/setup-python v5->v6: runs on Node24, changed default cache/registry behavior; python-version inputs unchanged.
• astral-sh/setup-uv v3->v8: spans several majors; enable-cache and version inputs still supported, cache key/save behavior changed. version "0.8.x" still honored.
• ytanikin/pr-conventional-commits 1.4.0->1.5.2: migrated to a Docker-based action (Linux runners only; this job is ubuntu-latest). task_types input still supported.

[claude]

nit: these two actions/setup-python@v4 references (lines 74 and 106) were left on v4, which runs on Node 16 — even older than the Node 20 versions this PR is bumping away from. They're inconsistent with the v5 -> v6.2.0 bump done in python.yml and with the PR's stated goal of clearing out pre-Node 24 actions. Recommend bumping both to actions/setup-python@v6.2.0 here as well. (not blocking)