ci: check user-facing crate semver

[mnkj0021]

Fixes #573.

Adds cargo-semver-checks to the existing wrapper/cache flow and a dedicated PR CI check for the user-facing crates requested in the issue discussion:

• wasefire-board-api (crates/board)
• wasefire-scheduler (crates/scheduler)
• wasefire (crates/prelude)

The check compares a crate whose version changed against the pull request base revision, using the public feature sets represented by each crate's docs configuration. Unchanged crates are skipped. It is also wired into scripts/ci.sh for local use.

Validation:

• sh -n scripts/ci-semver.sh scripts/ci.sh scripts/wrapper.sh: passed
• ./scripts/ci-copyright.sh: passed
• ./scripts/ci-semver.sh <upstream-main>: passed; all three unchanged crates skipped as expected
• temporary patch-version bumps for board, scheduler, and prelude: each built current and baseline APIs and passed 196/196 applicable SemVer checks
• negative control removing Impossible::unreachable from board with a patch bump: failed as expected with inherent_method_missing, requiring a major version bump
• git diff --check: passed
• ./scripts/ci-changelog.sh: not completed locally because this VPS lacks the system libudev development package required by the xtask dependency graph

AI coding-assistant assistance was used while preparing and validating this contribution. I reviewed the final diff and validation results and take responsibility for the submission.

[gemini-code-assist]

Code Review

This pull request introduces a new SemVer compatibility check for user-facing published crates (board, scheduler, and prelude) using cargo-semver-checks. The feedback recommends improving the robustness of the version extraction logic in scripts/ci-semver.sh by handling potential formatting variations in Cargo.toml and ensuring that version parsing failures do not silently bypass the SemVer checks.

[ia0]

Thanks a lot for the PR!