feat: support NUT-26 Bech32m-Encoded Payment Requests

[KvngMikey]

Fixes #857

Implements NUT-26 (Bech32m + TLV) encoding for payment requests as an alternative to the CBOR+base64 format (NUT-18).

• Bech32m encode/decode, TLV serialization, transport encoding (nostr + http_post), NUT-10 spending conditions, tag tuples
• deserialize() auto-detects creqb1 (NUT-26) vs creqA (NUT-18) and dispatches accordingly; added serialize_bech32m() method, case-insensitive prefix detection for both formats
• pay and decode commands accept both creqA and creqb1 prefixes
• Backward compatible as existing creqA serialization is untouched
• No new dependencies, reuses the existing bech32 package primitives with the Bech32m checksum constant (0x2BC830A3)

[codecov]

Codecov Report

❌ Patch coverage is 59.42029% with 112 lines in your changes missing coverage. Please review.
✅ Project coverage is 74.76%. Comparing base (89564fe) to head (5cf58d1).
⚠️ Report is 70 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
cashu/core/nuts/nut26.py	53.52%	112 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #904       +/-   ##
===========================================
+ Coverage   61.51%   74.76%   +13.25%     
===========================================
  Files          93      100        +7     
  Lines       11051    11950      +899     
===========================================
+ Hits         6798     8935     +2137     
+ Misses       4253     3015     -1238     

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[b-l-u-e]

Thanks for the PR but the commit history is pretty noisy ruff/CI fixes, merge commits, small follow-ups which makes the timeline harder to scan. Could you squash or reorganize into a few logical commits for example one for the feature, one for tests..

[KvngMikey]

Thanks for the PR but the commit history is pretty noisy ruff/CI fixes, merge commits, small follow-ups which makes the timeline harder to scan. Could you squash or reorganize into a few logical commits for example one for the feature, one for tests..

@b-l-u-e , perfect, this has been done now.

[b-l-u-e]

@b-l-u-e , perfect, this has been done now.

looks cleaner thanks

[b-l-u-e]

based on issue #857 it mentions mint compatibility wherever payment-request data is parsed or persisted. I couldn’t find creq*, nut18,or nut26 references under cashu/mint unless im doing it the wrong way

[KvngMikey]

based on issue #857 it mentions mint compatibility wherever payment-request data is parsed or persisted. I couldn’t find creq*, nut18,or nut26 references under cashu/mint unless im doing it the wrong way

The mint doesn't parse or persist payment request strings, payment requests are a wallet-to-wallet concept, the issue has been updated to reflect this.

[callebtc]

pls move the model definition into the centralized models file where all BaseModels are defined

[Copilot]

Pull request overview

Implements NUT-26 Bech32m+TLV encoding/decoding for payment requests, adds auto-detection in NUT-18 deserialize(), and updates the wallet CLI + tests to accept both NUT-18 (creqA) and NUT-26 (creqb1) formats.

Changes:

• Added cashu/core/nuts/nut26.py with Bech32m primitives, TLV serialization, and PaymentRequest encode/decode.
• Updated NUT-18 helpers and wallet CLI to decode either NUT-18 or NUT-26 payment requests.
• Added/updated wallet and CLI tests to cover NUT-26 vectors, round-trips, and validation cases.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 11 comments.

Show a summary per file

File	Description
cashu/core/nuts/nut26.py	New NUT-26 Bech32m+TLV codec implementation (including transport + NUT-10 encoding).
cashu/core/nuts/nut18.py	Refactors NUT-18 into serialize()/deserialize() functions and dispatches to NUT-26 on creqb1.
cashu/core/base.py	Moves PaymentRequest/Transport/NUT10Option models into shared core base module.
cashu/wallet/cli/cli.py	Extends pay/decode command handling to accept NUT-26 payment request strings.
tests/wallet/test_wallet_payment_request.py	Adds extensive NUT-26 serialization/deserialization/validation tests and updates NUT-18 tests to use new helpers.
tests/wallet/test_cli_nut26.py	New CLI-level tests for decode/pay using NUT-26 requests.
tests/wallet/test_cli_nut18.py	Updates CLI tests to use nut18.serialize() instead of PaymentRequest.serialize().

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