Migrate release workflow to shared package actions

[lukewilliamboswell]

Summary

• migrate the release workflow to roc-lang/release-package shared actions
• use setup-roc nightly-new-compiler and the release-package PR How to ignore result of a parser? #2 action refs while testing create-followup-pr
• remove Zig setup and use ubuntu-latest only for this pure package's bundle validation
• move release-time example URL rewriting to scripts/update_example_urls.py
• adjust runnable examples to avoid compile-time parse warnings under the current nightly
• clean up touched examples using the Roc style guide and roc fmt
• open a release follow-up PR for docs/examples instead of pushing directly to the protected base branch

Action refs

• roc-lang/setup-roc@bd311e2
• roc-lang/release-package/actions/*@3a25de642bce84c70b0f4ab6b30ee0f730acb5cf (Add release follow-up PR action roc-lang/release-package#2)

Verification

• PASS: roc fmt --check examples/csv-movies.roc examples/letters.roc examples/markdown.roc examples/numbers.roc
• PASS: Ruby YAML parse for .github/workflows/release.yml and .github/workflows/tests.yaml
• PASS: bash -n scripts/bundle.sh ci/all_tests.sh
• PASS: scripts/update_example_urls.py --help
• PASS: update_example_urls.py rewrites copied examples against a temporary bundle URL
• SKIPPED: actionlint is not installed locally

Repo-specific decisions

• Bundle testing is ubuntu-latest only because roc-parser is a pure package and does not require an OS/platform-host matrix.
• Keep bump_check: require.
• Preserve the existing xml-svg.roc skip because its migrated roc-html dependency is not available.
• Release docs still publish from www, and release follow-up changes are proposed through a PR because the base branch is protected.