* Refactor OidcTokenProvider to remove dependency on IdentityModel and improve token handling

* Improve OidcTokenProvider error handling and expiry setting

The constructor `OidcTokenProvider` now always sets the `_expiry`
field by calling `GetExpiryFromToken()`, regardless of whether
`_idToken` is null or empty, removing the previous check for a
non-empty `_idToken`.

The `GetExpiryFromToken` method has been updated to handle invalid
JWT token formats more gracefully. Instead of throwing an
`ArgumentException` when the token format is invalid or when the
'exp' claim is missing, the method now returns a default value.

The logic for parsing the JWT token and extracting the 'exp' claim
has been wrapped in a try-catch block. If any exception occurs
during this process, it is caught, and the method returns a default
value instead of throwing an exception.

* Refactor parts initialization inside try block

Moved the initialization of the `parts` variable, which splits the `_idToken` string, inside the `try` block. Removed the previous check for exactly three elements in the `parts` array and the default return value if the check failed.

* Add tests.

---------

Co-authored-by: Boshi Lian <farmer1992@gmail.com>