[FEAT] Amountless Melt Requests

[a1denvalu3]

Main Objective

Adds support for amountless payment requests (e.g. bolt11 amountless invoices)
and signals support in the info endpoint (mint features)

cashubtc/nuts#173

Enabled for:

• CLN
• LND
• Fake
• Blink
• LNbits
• Strike

Also Added

PaymentQuoteKind:

• REGULAR for regular quotes
• AMOUNTLESS for quotes where the amount is specified in the amountless option
• PARTIAL for quotes where we pay only the partial amount specified in the mpp option

m07_add_payment_quote_kind migration adds the kind column to melt_quotes in the DB. Defaults to REGULAR for all already present records.

[codecov]

Codecov Report

Attention: Patch coverage is 27.17949% with 142 lines in your changes missing coverage. Please review.

Project coverage is 52.50%. Comparing base (3e32dc4) to head (5e4aac8).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
cashu/lightning/clnrest.py	7.89%	35 Missing ⚠️
cashu/lightning/lnd_grpc/lnd_grpc.py	8.57%	32 Missing ⚠️
cashu/lightning/lndrest.py	8.57%	32 Missing ⚠️
cashu/lightning/fake.py	15.00%	17 Missing ⚠️
cashu/core/mint_info.py	18.18%	9 Missing ⚠️
cashu/wallet/wallet.py	25.00%	6 Missing ⚠️
cashu/wallet/v1_api.py	25.00%	3 Missing ⚠️
cashu/core/errors.py	81.81%	2 Missing ⚠️
cashu/mint/ledger.py	50.00%	2 Missing ⚠️
cashu/core/models.py	90.00%	1 Missing ⚠️
... and 3 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #712      +/-   ##
==========================================
- Coverage   55.36%   52.50%   -2.86%     
==========================================
  Files          84       84              
  Lines        9479     9652     +173     
==========================================
- Hits         5248     5068     -180     
- Misses       4231     4584     +353     

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[a1denvalu3]

There is a problem here: when paying, backends cannot distinguish whether the amount on the quote is a partial amount or the full amount for a amountless invoice.