refactor: add type hints to parser library and Laravel facades

[Ayoub-Mabrouk]

Adds type hints and property type declarations to improve type safety.

Parser Library:

• Added type hints to SignatureValidator::validateSignature() parameters and return type
• Replaced docblock annotations with property type declarations in ParsedEvents

Laravel:

• Added return type : string to all facade `getFacadeAcc

[eucyt]

@Ayoub-Mabrouk
Thank you for your contribution. The code looks good.

However, the CI is failing, so could you please fix it?

https://github.com/line/line-bot-sdk-php/actions/runs/21058965581/job/60560797406?pr=772#step:14:16

You also need to update the documentation following the steps below and commit the changes.

line-bot-sdk-php/.github/workflows/generate-code.yml

Lines 56 to 57 in b3dd73a

	wget https://github.com/phpDocumentor/phpDocumentor/releases/download/v3.8.1/phpDocumentor.phar
	php phpDocumentor.phar run -d src -t docs

[Ayoub-Mabrouk]

Thank you for your contribution. The code looks good.

Thanks @eucyt 😊

However, the CI is failing, so could you please fix it?

i fixed it, i noticed CONTRIBUTING.md explains how to generate docs, but not when you need to do it (like after merging from master) or that you must commit the changes. This caused me to miss regenerating the docs.

Would it be helpful if I opened a PR to:

1. Add a composer docs command to make it easier to regenerate
2. Update CONTRIBUTING.md to clearly explain when/why you need to regenerate and commit the docs

This might help prevent others from hitting the same CI failure. Should I go ahead with a PR?