Support cbor2 6

[nielstron]

Depends on #502 (fix/ci-pytest-command). That PR should be merged first; once it lands in main, this PR will contain only the cbor2 6 changes.

Summary

• require cbor2 6 or newer and Python 3.10 or newer (cbor2 6 requires at least 3.10)
• adapt serialization and CIP-8 decoding to the cbor2 6 public API
• preserve definite and indefinite CBOR array shapes for byte-exact Cardano transaction and datum round trips
• update dependency locks, CI versions, documentation, and tests

[codecov]

Codecov Report

❌ Patch coverage is 94.28571% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.79%. Comparing base (3bc5677) to head (bd70527).

Files with missing lines	Patch %	Lines
pycardano/serialization.py	93.25%	5 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #503      +/-   ##
==========================================
+ Coverage   90.73%   90.79%   +0.05%     
==========================================
  Files          37       37              
  Lines        5356     5422      +66     
  Branches      808      825      +17     
==========================================
+ Hits         4860     4923      +63     
- Misses        308      309       +1     
- Partials      188      190       +2     

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[Cerkoryn]

CBOR compatibility is an obstacle to simplifying dependencies in our defi-kernel trading engine: we currently pin cbor2 below 6 with a pure-Python build, and Dendrite pins PyCardano 0.18.0. We’re interested in this work landing with byte-exact transaction/datum preservation and a clear supported-version path; we’ll track this thread rather than open a duplicate.

[cffls]

Thanks, this is huge! Looks like it is backward incompatible, should be released with a major version bump I guess.

[nielstron]

Yes should neither introduce new behavior nor break old behavior.