Stable hash for determining if input specification changed

[manuelbl]

Fixes #24644

For the Maven plugin to reliably detect if the input specification has changed, the fully parsed specification is written to a buffer (as JSON) and the hash is computed from the result.

Before, the hash was computed by calling toString() on the parsed specification, which is not stable for all possible elements of a specification. In particular, binary data provides as an example for a property of type string / format byte was not stable.

(I'm not sure why one of the pom.xml files. See the second changed file in this PR. It's a side-effect of running generate-samples.sh.)

PR checklist

• Read the contribution guidelines.
• Run the following to build the project and update samples:

  ./mvnw clean package || exit
  ./bin/generate-samples.sh ./bin/configs/*.yaml || exit
  ./bin/utils/export_docs_generators.sh || exit
  

  (For Windows users, please run the script in WSL)
  Commit all changed files.
  This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master.
  These must match the expectations made by your contribution.
  You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example ./bin/generate-samples.sh bin/configs/java*.
  IMPORTANT: Do NOT purge/delete any folders/files (e.g. tests) when regenerating the samples as manually written tests may be removed.
• If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request.

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Summary by cubic

Stabilizes input spec change detection in the Maven plugin by hashing the JSON-serialized OpenAPI model instead of toString(). Unparsable specs now yield a unique hash to avoid skipping generation steps.

• Bug Fixes

  • Compute SHA-256 from Jackson-serialized OpenAPI (v3.0 uses Json.mapper(), v3.1 uses Json31.mapper()).
  • Return a unique "INVALID-HASH-..." when parsing fails to ensure downstream steps still run.

• Dependencies

  • Sample resttemplate-springBoot4-jackson3: set spring-web-version to 7.0.5.

^{Written for commit a1e0eac. Summary will update on new commits.}

[cubic-dev-ai]

All reported issues were addressed across 2 files

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