test: Fuzz the human-readable part of bech32 as well #30623

1. 
   paplorinc commented at 7:56 am on August 10, 2024: contributor

   Split out of https://github.com/bitcoin/bitcoin/pull/30596/files#r1706957219

   Instead of the static “bc” human-readable part, it’s now randomly generated based on https://github.com/bitcoin/bips/blob/master/bip-0173.mediawiki and the extra restrictions in the code:

   The human-readable part, which is intended to convey the type of data, or anything else that is relevant to the reader. This part MUST contain 1 to 83 US-ASCII characters, with each character having a value in the range [33-126]. HRP validity may be further restricted by specific applications.

   Since bech32::Encode rejects uppercase letters, we’re actually generating values in the [33-126] - ['A'-'Z'] range.

2. Split out bech32 separator char to header 988eb2f8ff
3. 
   DrahtBot commented at 7:56 am on August 10, 2024: contributor

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4. DrahtBot added the label Tests on Aug 10, 2024
5. DrahtBot added the label CI failed on Aug 10, 2024
6. Fuzz HRP of bech32 as well

   Also separated the roundtrip testing from the random string decoding for clarity
   
   Note that while BIP 173 claims:
   ```
   The human-readable part, which is intended to convey the type of data, or anything else that is relevant to the reader. This part MUST contain 1 to 83 US-ASCII characters, with each character having a value in the range [33-126]. HRP validity may be further restricted by specific applications.
   ```
   bech32::Encode rejects uppercase letters.

   0c5bba5313
7. paplorinc force-pushed on Aug 10, 2024
8. DrahtBot removed the label CI failed on Aug 10, 2024
9. paplorinc marked this as ready for review on Aug 18, 2024

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