Multiple test and test utils migrations to TS

[matux]

Description of the change

This PR migrates test files and test utilities from JavaScript to TypeScript by updating file extensions and import paths from .js to .ts, and refactors global type declarations for better organization.

Key changes:

• Updated import paths across test files to reference .ts extensions instead of .js for test utilities and fixtures
• Migrated fixture files (locals.fixtures, payloads.fixtures, rrwebEvents.fixtures, etc.) to TypeScript
• Relocated global type declarations from browser.rollbar.test-utils.ts to a centralized test/index.ts file

[Copilot]

Pull request overview

This PR migrates test files and test utilities from JavaScript to TypeScript by updating file extensions and import paths from .js to .ts, and refactors global type declarations for better organization.

Key changes:

• Updated import paths across test files to reference .ts extensions instead of .js for test utilities and fixtures
• Migrated fixture files (locals.fixtures, payloads.fixtures, rrwebEvents.fixtures, etc.) to TypeScript
• Relocated global type declarations from browser.rollbar.test-utils.ts to a centralized test/index.ts file

Reviewed changes

Copilot reviewed 22 out of 26 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
test/util/timers.ts	Updated documentation examples and added TypeScript generics to setTimeout function
test/index.ts	New file containing centralized global type declarations for test utilities
test/browser.rollbar.test-utils.ts	Removed global type declarations (moved to test/index.ts)
test/fixtures/locals.fixtures.ts	Changed variable declaration from var to const
test/fixtures/replay/index.ts	Updated imports to use .ts extensions
test/examples/*.test.ts	Updated imports for test utilities to use .ts extensions
test/replay/integration/*.test.js	Updated fixture imports to use .ts extensions
test/replay/util/mockRecordFn.js	Updated fixture imports to use .ts extensions
test/tracing/exporter.toPayload.test.js	Updated fixture imports to use .ts extensions
test/server.locals.merge.test.js	Updated fixture imports to use .ts extensions
test/browser.*.test.ts	Updated timer utility imports to use .ts extensions

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