fix: enabling eslint ban-types rule and fixed string typing

[joker23]

This PR reenables the ban-type eslint rule. This results in:

• a fix to a pre-existing typing bug where String type should be string
• a more defined Function typing

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Note

Low Risk
Mostly TypeScript typing/lint-only changes (replacing Function/String with safer types) with minimal runtime impact; risk is limited to potential downstream type incompatibilities in event listener signatures.

Overview
Re-enables stricter TypeScript linting around banned types by removing the global @typescript-eslint/ban-types opt-out and adding targeted suppressions where Function return types are required (e.g. listeners()/rawListeners()).

Tightens public and test-facing callback typings across clients/emitter APIs by replacing Function with (...args: any[]) => void, and fixes boxed String usages to primitive string in request bodies and transactional store selector parameters (plus deepCompact now constrains T to object).

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[github-actions]

@launchdarkly/js-sdk-common size report
This is the brotli compressed size of the ESM build.
Compressed size: 25623 bytes
Compressed size limit: 29000
Uncompressed size: 125843 bytes

[github-actions]

@launchdarkly/js-client-sdk size report
This is the brotli compressed size of the ESM build.
Compressed size: 31858 bytes
Compressed size limit: 34000
Uncompressed size: 113634 bytes

[github-actions]

@launchdarkly/js-client-sdk-common size report
This is the brotli compressed size of the ESM build.
Compressed size: 38473 bytes
Compressed size limit: 39000
Uncompressed size: 211104 bytes

[github-actions]

@launchdarkly/browser size report
This is the brotli compressed size of the ESM build.
Compressed size: 179574 bytes
Compressed size limit: 200000
Uncompressed size: 830815 bytes

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 3 additional findings.