fix: struct metadata parsing for nested decimal fields

[sshpuntoff]

Description

When parsing Struct<Decimal(10,20)>, the driver currently raises an exception:

  java.lang.ArrayIndexOutOfBoundsException: Index 1 out of bounds for length 1
      at com.databricks.jdbc.api.impl.MetadataParser.parseStructMetadata(MetadataParser.java:30)
      at com.databricks.jdbc.api.impl.ComplexDataTypeParser.parseToStruct(ComplexDataTypeParser.java:104)
      at com.databricks.jdbc.api.impl.ComplexDataTypeParser.convertValueNode(ComplexDataTypeParser.java:131)
      at com.databricks.jdbc.api.impl.ComplexDataTypeParser.parseToArray(ComplexDataTypeParser.java:73)

This occurs because the current implementation does not expect nested comma's in datatypes.
By tracking the Depth of the () characters, we can successfully parse complex datatypes.

Issue:
#981

Testing

Unit tests expanded and local testing done.

Additional Notes to the Reviewer

This is a bug in the implementation of the MetaDataParser and is pretty direct to re-produce and correct.

[sshpuntoff]

there is a case to be made that just a single
int depth = 0; would work correctly here, and the code below just needs to be

if (ch == '<' || ch == '(') {
 depth ++;
}
else if (ch == '>' || ch == ')') {
    depth --;
}

Which would simplify the change set even more.
Let me know if you prefer a minimal diff over the explicit variable names.

[josecsotomorales]

@jayantsing-db can we get a review on this PR? 🙏🏻

[jayantsing-db]

Thanks, approved. I will take care of merging it.

[Copilot]

Pull Request Overview

This PR fixes a bug in the JDBC driver's metadata parsing for nested decimal fields within struct types. The driver was failing with an ArrayIndexOutOfBoundsException when parsing complex struct metadata containing decimal types with precision and scale parameters due to improper comma splitting that didn't account for parentheses depth.

• Fixed the splitFields method to track both angle bracket and parentheses depth when parsing struct metadata
• Added comprehensive test coverage for various combinations of decimal fields in struct types

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/main/java/com/databricks/jdbc/api/impl/MetadataParser.java	Enhanced field splitting logic to properly handle parentheses depth alongside angle bracket depth
src/test/java/com/databricks/jdbc/api/impl/MetadataParserTest.java	Added 6 new test cases covering decimal fields in simple, nested, and complex struct scenarios

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