[PR] [common] Fix nested field IDs in Schema.Builder.fromColumns [fluss]

["gyang94 (via GitHub)" <gi...@apache.org>]

gyang94 opened a new pull request, #4725:
URL: https://github.com/apache/fluss/pull/4725

   ### Purpose
   
   Closes #4724.
   
   `Schema.Builder.fromColumns` leaves nested row field IDs unset when all input column IDs are unknown (`-1`). Multiple nested fields then fail the global ID uniqueness check. Assign IDs across the full nested structure using the builder's shared counter.
   
   ### Brief change log
   
   - Reuse `ReassignFieldId` when adopting columns with unknown IDs.
   - Add a regression test for multiple row nesting levels, subsequent column allocation, column metadata, and unchanged input columns.
   - Clarify when `fromColumns` preserves or assigns IDs.
   
   ### Tests
   
   - Confirmed the new regression test fails before the fix: `Found 4 unique IDs but expected 6`.
   - `mvn -B -pl fluss-common -am spotless:apply verify` passed with Maven 3.8.6 and JDK 11, including Spotless, Checkstyle, and RAT.
   - Test reports: `fluss-common` — 2,064 tests, 1 skipped; `fluss-test-utils` — 11 tests, 3 skipped. No failures or errors.
   
   ### API and Format
   
   No public API signatures or serialized formats change. Columns with assigned IDs retain their existing IDs.
   
   ### Documentation
   
   Updated the `fromColumns` Javadoc.
   
   Generative AI disclosure: OpenAI Codex was used to author the implementation and regression test.
   


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