feat(flagd-core): update fractional operator to CBOR encoding (v3)

[m-olko]

This PR

Update fractional bucketing in openfeature-flagd-core to use canonical CBOR encoding and unsigned 32-bit MurmurHash3 per the latest flagd specification.

• Implement number normalization for float/int consistency per specification

• Support non-string targeting keys and null bucketing keys returning None

• Use [flagKey, targetingKey] CBOR array for shorthand bucketing syntax

• Update flagd-testbed submodule to v3.10.1 and select @fractional-v3 tests

• Add unit tests for null handling, zero equivalence, float equivalence, and ordering

Related Issues

Fixes #324

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[codecov]

Codecov Report

❌ Patch coverage is 89.28571% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.57%. Comparing base (92c5f49) to head (6d6c3f2).

Files with missing lines	Patch %	Lines
...e/contrib/tools/flagd/core/targeting/custom_ops.py	89.28%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #415      +/-   ##
==========================================
- Coverage   95.64%   93.57%   -2.08%     
==========================================
  Files          24       31       +7     
  Lines        1057     1089      +32     
==========================================
+ Hits         1011     1019       +8     
- Misses         46       70      +24     

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