Update dependency Flask to v3

This MR contains the following updates:

Package	Update	Change
Flask (changelog)	major	==2.3.3 -> ==3.0.3

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Release Notes

pallets/flask (Flask)

v3.0.3

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Released 2024-04-07

• The default hashlib.sha1 may not be available in FIPS builds. Don't access it at import time so the developer has time to change the default. :issue:5448
• Don't initialize the cli attribute in the sansio scaffold, but rather in the Flask concrete class. 🇵🇷5270

v3.0.2

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Released 2024-02-03

• Correct type for jinja_loader property. :issue:5388
• Fix error with --extra-files and --exclude-patterns CLI options. :issue:5391

v3.0.1

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Released 2024-01-18

• Correct type for path argument to send_file. :issue:5230
• Fix a typo in an error message for the flask run --key option. 🇵🇷5344
• Session data is untagged without relying on the built-in json.loads object_hook. This allows other JSON providers that don't implement that. :issue:5381
• Address more type findings when using mypy strict mode. 🇵🇷5383

v3.0.0

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Released 2023-09-30

• Remove previously deprecated code. 🇵🇷5223
• Deprecate the __version__ attribute. Use feature detection, or importlib.metadata.version("flask"), instead. :issue:5230
• Restructure the code such that the Flask (app) and Blueprint classes have Sans-IO bases. 🇵🇷5127
• Allow self as an argument to url_for. 🇵🇷5264
• Require Werkzeug >= 3.0.0.

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