Spanner bulk data migration: Add support for DECIMAL as a primary key

[nmemond]

This is a copy of #3087 but up-to-date with main and with issues fixed, because that developer is out of office for the rest of the year and I don't have permissions to push to their fork.

[gemini-code-assist]

Summary of Changes

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This pull request introduces robust support for DECIMAL data types when they are used as primary keys in source databases for Spanner bulk data migration. It addresses the need to accurately represent and partition DECIMAL values by integrating their numericScale into the data processing pipeline. This ensures that migrations involving tables with DECIMAL primary keys are performed correctly and efficiently, preventing data integrity issues and improving the overall reliability of the migration process.

Highlights

• DECIMAL Primary Key Support: The Spanner bulk data migration tool now supports DECIMAL data types as primary keys, enhancing its compatibility with source databases that utilize this type for indexing.
• Numeric Scale Handling: The system has been updated to correctly extract and utilize the numericScale property of DECIMAL columns, which is crucial for accurate partitioning and splitting of BigDecimal values during data migration.
• Refactored BigDecimal Splitting Logic: The internal BigDecimal splitting mechanism has been refactored to incorporate the numericScale, ensuring that split points are calculated precisely according to the decimal precision of the column.
• Comprehensive Testing: New unit and integration tests have been added to validate the correct handling of DECIMAL primary keys, including schema discovery, boundary extraction, and splitting logic, along with updated MySQL and Spanner schema definitions.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 55.88%. Comparing base (d34cbde) to head (4497991).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #3119      +/-   ##
============================================
+ Coverage     50.54%   55.88%   +5.34%     
+ Complexity     5047     1642    -3405     
============================================
  Files           974      471     -503     
  Lines         59808    26523   -33285     
  Branches       6523     2781    -3742     
============================================
- Hits          30230    14823   -15407     
+ Misses        27443    10802   -16641     
+ Partials       2135      898    -1237     

Components	Coverage Δ
spanner-templates	71.85% <100.00%> (+1.07%)	⬆️
spanner-import-export	∅ <ø> (∅)
spanner-live-forward-migration	80.04% <ø> (ø)
spanner-live-reverse-replication	77.68% <ø> (-0.05%)	⬇️
spanner-bulk-migration	88.28% <100.00%> (+0.02%)	⬆️

Files with missing lines	Coverage Δ
...jdbc/dialectadapter/mysql/MysqlDialectAdapter.java	99.62% <100.00%> (+<0.01%)	⬆️
...source/reader/io/jdbc/iowrapper/JdbcIoWrapper.java	92.93% <100.00%> (+0.03%)	⬆️
...reader/io/jdbc/uniformsplitter/range/Boundary.java	98.46% <100.00%> (+0.07%)	⬆️
...uniformsplitter/range/BoundarySplitterFactory.java	100.00% <100.00%> (ø)
...io/jdbc/uniformsplitter/range/PartitionColumn.java	94.73% <100.00%> (+1.87%)	⬆️
...source/reader/io/schema/SourceColumnIndexInfo.java	69.23% <100.00%> (+1.23%)	⬆️

... and 522 files with indirect coverage changes

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[VardhanThigle]

Please rebase This PR on top of the tree code.