Feature/Add common interface for padding

[Kalkwst]

I have added a new interface IBlockCipherPadding that defines the methods that an algorithm that implements block cipher padding must follow. This will allow to have a more organized and structured codebase regarding padding algorithms that can be used in block ciphers.

I have also added a new InvalidPaddingException to better convey issues within the padding algorithms, such as invalid padding length or format.

This PR is related to issue #410

• I have performed a self-review of my code
• My code follows the style guidelines of this project
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Comments in areas I changed are up to date
• I have added comments to hard-to-understand areas of my code
• I have made corresponding changes to the README.md

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (60d4de0) 96.10% compared to head (da3d488) 96.12%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #420      +/-   ##
==========================================
+ Coverage   96.10%   96.12%   +0.02%     
==========================================
  Files         234      234              
  Lines        9843     9843              
==========================================
+ Hits         9460     9462       +2     
+ Misses        383      381       -2     

Files	Coverage Δ
Algorithms/Crypto/Paddings/Iso10126D2Padding.cs	100.00% <ø> (ø)
Algorithms/Crypto/Paddings/Iso7816D4Padding.cs	100.00% <ø> (ø)
Algorithms/Crypto/Paddings/Pkcs7Padding.cs	100.00% <ø> (+3.44%)	⬆️
Algorithms/Crypto/Paddings/TbcPadding.cs	100.00% <ø> (ø)
Algorithms/Crypto/Paddings/X932Padding.cs	100.00% <ø> (ø)

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[siriak]

Looks good, thanks!