refactor: update pipe transform signatures for improved type safety

[miso-kyoungminkim]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

What is the current behavior?

Issue Number: N/A

This PR imporoves the type safety of built-in pipes in the @nestjs/common package by refining input/output types and removing unnecessary type assertions.

• Introduction of unknown Input Type: Updated the transform method in all pipes to accept value: unknown instead of any or specific types like string. This forces more explicit type checking before processing the input.
• Refined Return Types: Updated the return types of transform methods to explicitly include null | undefined when the optional configuration is enabled, accurately reflecting the pipe's potential output.
• Robust Validation Logic: Replaced any assertions with explicit type guards (e.g., isString, isNumber, instanceof Date) to ensure data integrity.
• Consistent Implementation: Applied these improvements across the entire pipe collection.
• Theses changes preserve backward compatibility and pass all existing tests.

What is the new behavior?

nothing changed

Does this PR introduce a breaking change?

• Yes
• No

Other information

[coveralls]

Pull Request Test Coverage Report for Build 92fc9ffa-d560-4892-b2fe-2aff2db6e7d0

Details

• 16 of 16 (100.0%) changed or added relevant lines in 9 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 89.759%

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Totals
Change from base Build 2ad1776b-4e80-4104-bc1d-47efd0095c0f:	0.0%
Covered Lines:	7441
Relevant Lines:	8290

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💛 - Coveralls