Mistakes have been made. I forgot about a bunch of `todo`s in the helper
functions. So, this PR replaces them with proper errors. It also adds
tests for parse-time evaluation, because one `todo` I missed was in a
`run_const` function.
Based on the discussion in #13419.
## Description
Reworks the `decode`/`encode` commands by adding/changing the following
bases:
- `base32`
- `base32hex`
- `hex`
- `new-base64`
The `hex` base is compatible with the previous version of `hex` out of
the box (it only adds more flags). `base64` isn't, so the PR adds a new
version and deprecates the old one.
All commands have `string -> binary` signature for decoding and `string
| binary -> string` signature for encoding. A few `base64` encodings,
which are not a part of the
[RFC4648](https://datatracker.ietf.org/doc/html/rfc4648#section-6), have
been dropped.
## Example usage
```Nushell
~/fork/nushell> "string" | encode base32 | decode base32 | decode
string
```
```Nushell
~/fork/nushell> "ORSXG5A=" | decode base32
# `decode` always returns a binary value
Length: 4 (0x4) bytes | printable whitespace ascii_other non_ascii
00000000: 74 65 73 74 test
```
## User-Facing Changes
- New commands: `encode/decode base32/base32hex`.
- `encode hex` gets a `--lower` flag.
- `encode/decode base64` deprecated in favor of `encode/decode
new-base64`.
