Fix release version replacement appending old suffixes

[Copilot]

The release automation was generating chained artifact versions like 1.0.0-beta-java.3-beta-java.2-beta-java.1 and duplicate [Unreleased] link definitions in CHANGELOG.md because the version qualifier regex didn't recognize the -beta-java.N format.

Root causes

sed patterns (publish-maven.yml) — BRE group syntax bug: (beta-) was treated as a literal string (beta-) rather than an optional group. Pattern only matched the base M.M.P, then the new qualifier was appended, leaving the old suffix intact:

# Before (only matched base M.M.P):
\(-java\(-preview\)\{0,1\}\.[0-9][0-9]*\)\{0,1\}

# After (matches any number of -word.N qualifiers, including chained ones):
\(-[a-z][a-z0-9-]*\.[0-9][0-9]*\)*

awk script (update-changelog.sh) — Two bugs:

1. The [Unreleased]: URL regex extracted only the base version, so the new version link pointed to the wrong predecessor (e.g., v0.3.0-java.2 instead of v1.0.0-beta-java.2).
2. Both the [Unreleased]: handler and the first-version-link handler could fire in the same run, each inserting a new [Unreleased]: definition.

Fixes

• publish-maven.yml: Replaced all sed version patterns with \(-[a-z][a-z0-9-]*\.[0-9][0-9]*\)* — matches -java.N, -java-preview.N, -beta-java.N, and also cleans up pre-existing chained versions. Updated version validation regex to accept -beta-java.N.
• update-changelog.sh: Extended awk version regex to (-(beta-)?java(-preview)?.[0-9]+)?; added unreleased_link_handled flag to prevent double-insertion of [Unreleased] links; reordered the two awk blocks so the flag is set before the first-version-link block evaluates it.
• CHANGELOG.md: Removed 18 duplicate [Unreleased] entries; corrected predecessor links for 1.0.0-beta-java.2 and 1.0.0-beta-java.3.
• README.md, jbang-example.java, cookbook *.md: Replaced chained invalid versions with correct 1.0.0-beta-java.3.
• test-update-changelog.sh: Fixed pre-existing set -e + ((passed++)) bug that caused only one test to run; added tests for -beta-java.N format and duplicate-link prevention.

Pull request checklist

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)
• mvn spotless:apply has been run to format the code
• mvn clean verify passes locally

Does this introduce a breaking change?

• Yes
• No

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