Add integration tests to bulk spanner migration for checking MySQL data type support

[nmemond]

This adds some missing data type mappings to the existing data type integration test, and also adds a test for a migration to a postgres dialect spanner instance.

Note that some of the type mappings fail to migrate as expected. The checks for those are still included for completeness, but they're commented out to avoid failing the tests.

[gemini-code-assist]

Summary of Changes

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This pull request significantly enhances the integration test suite for bulk Spanner migrations by broadening the range of MySQL data types covered and introducing a dedicated test for migrations targeting PostgreSQL dialect Spanner instances. These changes aim to improve the robustness and reliability of the migration process by verifying data integrity across a wider array of data type conversions and different Spanner configurations.

Highlights

• Expanded MySQL Data Type Coverage: The existing integration test for MySQL data types has been significantly expanded to include numerous new type mappings, such as various _to_string conversions (e.g., bigint_to_string, decimal_to_string, datetime_to_string), bit_to_bool, bit_to_int64, and json_to_string, among others. This ensures more comprehensive testing of data migration capabilities.
• PostgreSQL Dialect Spanner Integration Test: A new integration test has been added specifically for migrating data from MySQL to a PostgreSQL dialect Spanner instance. This new test validates the data type conversions and migration process for Spanner instances configured with PostgreSQL compatibility.
• Test Infrastructure Improvements: The test setup and teardown logic in MySQLDataTypesIT.java has been refined. Resource managers are now initialized only once per test class using a synchronized block and an initialized flag, improving efficiency. Cleanup now includes the newly introduced PostgreSQL dialect Spanner resource manager.
• Handling of Failing Type Mappings: The pull request notes that some type mappings fail to migrate as expected. These checks are still included in the test for completeness but are commented out to prevent test failures, indicating areas for future investigation or known limitations.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 55.65%. Comparing base (40b4a35) to head (44a9e9c).
⚠️ Report is 19 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #3046      +/-   ##
============================================
+ Coverage     50.41%   55.65%   +5.24%     
+ Complexity     5021     1614    -3407     
============================================
  Files           969      467     -502     
  Lines         59547    26321   -33226     
  Branches       6493     2766    -3727     
============================================
- Hits          30018    14650   -15368     
+ Misses        27406    10781   -16625     
+ Partials       2123      890    -1233     

Components	Coverage Δ
spanner-templates	71.62% <ø> (+1.02%)	⬆️
spanner-import-export	∅ <ø> (∅)
spanner-live-forward-migration	80.02% <ø> (ø)
spanner-live-reverse-replication	77.49% <ø> (ø)
spanner-bulk-migration	88.27% <ø> (+<0.01%)	⬆️
see 521 files with indirect coverage changes

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[VardhanThigle]

In this particular case I might request to add a new test class than overload existing one. There could be cases where there's support missing on PG side for which we have support on MySQL side (or vice versa)

For example in current PR, PG_FLOAT4 is not yet supported.

Can we add a new test Class for MySQL to PG dialect test (with it's own copy of schemas)?

When you add a new test class, for now, you can skip PG_FLOAT4 and we can fix that separately.