Refactor the converter table in Texture2DConverter

[isHarryh]

Summary

This PR refactors the CONV_TABLE and it related code.

• Before: { TF -> (function, arg1, arg2, ...) }
• After: { TF -> (function, (arg1, arg2, ...)) }

This PR also:

1. Fixes a typo (that could cause error) in CONV_TABLE where EAC_R:SIGNED should be EAC_R_SIGNED.
2. Changes the fmt argument of etc function to maintain consistency with eac.

Rationality

1. Clearly separate function and its additional arguments.

2. Resolves typing_extensions import error.
   In 035cb09 , typing_extensions package has been introduced to Texture2DConverter to provide the Unpack type hint. However, this package is not a standard library, so it is not installed in some Python environments, causing ModuleNotFoundError. Adding this package to UnityPy's dependencies explicitly can solve this error, but it is not worth it.

This PR is a part of #318