feat!: add padding support & make it optional

[grjte]

Description

This PR makes it possible to handle encoding/decoding of correctly padding base64 (which previously wasn't supported) or to optionally encode/decode base64 for which the padding has already been stripped.

Additionally, this PR again reformats to the most updated version.

Problem*

The standard encoding for base64 specifies padding, which isn't handled in this library and may be needed in some cases by default. However, since it will be more efficient without handling padding in cases where that's available, it's nice to make this optional

Summary*

• splits encoder/decoder into modules
• adds optional padding to encoder & decoder
• adds tests for each
• handles new formatting

Additional Context

PR Checklist*

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt on default settings. (used nargo fmt)

[grjte]

1. It turns out that the way I've architected (with globals for the different encoder/decoder options) this is not possible before v0.35.0. I bumped the compiler version, but "Test on Nargo 0.34.0" is listed as a required workflow step, so maybe another approach is needed. Lmk
2. I had formatted this with the nightly compiler to avoid the issue that came up last time, but it's not formatted correctly for v0.35.0. Please let me know what you prefer here (I'm guessing I should just format on v0.35.0, but I'd prefer to get feedback before running the workflow again)

[saleel]

Test on Nargo 0.34.0 Expected — Waiting for status to be reported

This seems to be a github bug that I have seen happen before as well - closing the PR and opening again fixes it sometimes. Let me try

Update: No, didnt work. I will check this, but for the other issue, maybe we can try upgrading to 0.36 now?

[TomAFrench]

I've updated the branch protection rules so this PR can go through. @saleel can you review?

[saleel]

I think this could be result[OutputElements - 1] = BASE64_PADDING_CHAR;

along with something like assert((InputBytes + 2) / 3 * 4 == OutputElements); at the top.