fix(typescript): infer nullable INTERVAL columns as string | null

[MuzzaiyyanHussain]

Fixes #1030

Problem

When generating TypeScript types, nullable INTERVAL columns are currently inferred as string
instead of string | null. This breaks type safety because the database allows NULL values
but the generated types do not reflect that.

Changes

• Updated TypeScript type generation to correctly respect is_nullable for INTERVAL columns
• Added tests to ensure nullable INTERVAL fields are typed as string | null

Result

Developers now get accurate TypeScript types that match the database schema,
preventing runtime null issues and improving overall type safety.

[MuzzaiyyanHussain]

@avallete

[avallete]

Thank's for your contribution !

Added an e2e test to ensure it works for both nullable and not nullable fields, and check the final type generated result.

[coveralls]

Pull Request Test Coverage Report for Build 20807237661

Details

• 3 of 3 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.002%) to 83.907%

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Totals
Change from base Build 20160694137:	0.002%
Covered Lines:	6258
Relevant Lines:	7343

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💛 - Coveralls

[avallete]

cc @o-santi @silentworks might be a better type for this in Python, mapping to str as it's the format for Typescript. WDYT ?

[MuzzaiyyanHussain]

@soedirgo ?