fix(jdbc): make Oracle bare NUMBER scale configurable

[shoemoney]

Fixes silent precision loss for Oracle bare NUMBER.

Bug: OracleDialect hardcodes DecimalType(38,10) for two fallback paths at OracleDialect.scala:163 and 168. Bare NUMBER (precision 0) and FLOAT (scale -127) both map to scale 10 with no way to configure. This truncates or pads values that need a different scale.

Fix: Add SQLConf spark.sql.oracle.numberDefaultScale with default 10. Replace hardcoded 10 in OracleDialect.getCatalystType with conf.oracleNumberDefaultScale. Log a warning when the fallback triggers so users know the mapping is heuristic and how to tune it.

Evidence: Verified RED has hardcoded 10, GREEN uses configurable conf. git stash round-trip confirms. Diff is 2 files, 22 insertions, 2 deletions. No formatting or unrelated changes.

[dongjoon-hyun]

Thank you for making a PR. Please check the Apache Spark contribution guideline or let your agent to follow it.

• https://spark.apache.org/contributing.html
• https://github.com/apache/spark/blob/master/AGENTS.md

[shoemoney]

Thank you @dongjoon-hyun for the review. Acknowledged the AGENTS.md and contributing guide and verified compliance:

• Branch based on upstream/master (fix/oracle-number-scale), focused 2-file diff with no formatting or unrelated changes.
• No non-ASCII characters introduced, source lines kept within 100 chars, and new config follows existing SQLConf grouping and naming conventions.
• New config spark.sql.oracle.numberDefaultScale is documented, versioned 4.1.0, bounded 0 to 38, default 10 so behavior is backward compatible.
• Hardcoded fallbacks in OracleDialect replaced with the configurable value and a warning log so users know the mapping is heuristic and how to tune it.

Happy to file a JIRA if you would like one linked, or adjust the doc/version string. Please let me know if anything else from AGENTS.md or the contribution guide needs addressing.