feat: add types

[Phillip9587]

This PR adds type definitions to finalhandler. It includes the following changes:

• added types
• adding type, main and types field to package.json
• adding a tsconfig.json which extends @tsconfig/node18 from https://github.com/tsconfig/bases
• adding type tests with @arethetypeswrong/cli and expect-type and run them in the CI Pipeline

Ref: expressjs/typescript-wg#1

cc @RobinTail

[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	@​tsconfig/​node18@​18.2.4
	expect-type@​1.2.2
	@​types/​node@​18.19.130
	@​arethetypeswrong/​cli@​0.18.2
	typescript@​5.9.3

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[Phillip9587]

@jonchurch @bjohansebas @clicktodev Could you please take a look at this PR when you get a chance? It’s part of the TypeScript WG initiative, and since we’re members, your input would be valuable.

[bjohansebas]

Actually, I think this should be targeted at version 2, since that’s the one being depended on. These changes can be backported to version 3

[Phillip9587]

@bjohansebas I recommend merging this into v3. If it turns out to be necessary, we can backport it to v2 afterwards.

[clicktodev]

the advantage of releasing this as a new major release is that people will be more likely to read the patch notes since it's a major release and they will discover that they shouldn't install third party types anymore.
the only problem with releasing the types in the existing release is that it may conflict with third party types.