refactor: Add missing month constants `September` and `October`

test: Improve unit test

test: nil loc -> nil location

test: Optimize unit test of `Scan` method

refactor: Add comment for `invalidPersianError`

test: Set a fixed time as the current time

docs: Update time formatting example

fix: Add a check for invalid dates before setting language objects

docs: update translation list in the README

refactor: rename `GetDefault` to `getDefault`