Pin rcgen to 0.14.7 for Rust 1.75

[wyfo]

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Labels: dependencies

📦 Dependency Updates

Since this PR updates dependencies:

• Changelog reviewed - Breaking changes in dependency identified and addressed
• Security advisories checked - No known vulnerabilities in new version
• License compatible - New version license is compatible with project
• Tests pass - All tests pass with new dependency versions
• Transitive deps reviewed - New transitive dependencies checked
• Version pinned appropriately - Semver range is intentional and correct
• Update scope limited - Updating one major dependency at a time when possible

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[wyfo]

Closing as duplicate — the change is already included in #2597.