Support nullable and non-nullable types with same name in the same template

[pengpeng-lu]

Modify TypeRepository to allow registering 2 types (only different in nullability) in the same schema template.
Use Case:
If we have struct A, and array of A in the same template, A is nullable, while A in the array is non-nullable. This should be allowed.

[github-actions]

📊 Metrics Diff Analysis Report

Summary

• New queries: 5
• Dropped queries: 0
• Plan changed + metrics changed: 0
• Plan unchanged + metrics changed: 0

ℹ️ About this analysis

This automated analysis compares query planner metrics between the base branch and this PR. It categorizes changes into:

• New queries: Queries added in this PR
• Dropped queries: Queries removed in this PR. These should be reviewed to ensure we are not losing coverage.
• Plan changed + metrics changed: The query plan has changed along with planner metrics.
• Metrics only changed: Same plan but different metrics

The last category in particular may indicate planner regressions that should be investigated.

New Queries

Count of new queries by file:

• yaml-tests/src/test/resources/struct-type-nullability-variants.metrics.yaml: 5