Fix/12 hour format validation

[Sho-ki]

Fix issue: #1625

Description of the Bug

The DateTime.fromFormat() function incorrectly validates certain 24-hour formats as valid when they should be considered invalid.
When using the 12-hour (h) format in the format parameter, the function does not properly invalidate times where the hour exceeds 12.

Actual vs Expected Behavior

DateTime.fromFormat('18:30 AM', 'h:mm a').isValid;

Actual: isValid returns true for DateTime.fromFormat('18:30 AM', 'h:mm a').
Expected: isValid shouldn't be true because 18 is not a valid hour for the 12-hour (h) format.

Fix Description

This PR addresses the issue by ensuring that when the 12-hour (h) format is used in the format parameter, any hour value greater than 12 is considered invalid, and isValid will throw error.

[linux-foundation-easycla]

• ✅login: Sho-ki / (d35be5a)
• ✅login: Sho-ki / (d35be5a, f8ae891)

The committers listed above are authorized under a signed CLA.

[diesieben07]

While this is a valid bugfix, I am reluctant to merge this in and release it as a minor update, because it is technically a breaking change. Normally that would be fine for a bug fix, but I can imagine many people intentionally or unintentionally relying on this behavior. Maybe we should add a strictHours option for backwards compatibility?

What do you think, @icambron?

[jw642459986]

@diesieben07 are you suggesting something like this?
DateTime.fromFormat('18:30 AM', 'h:mm a').isValid('strictHours': true);