ci: add Python 3.14 to test matrix

[polaz]

Add Python 3.14 to the unit test matrix in ci.yml alongside 3.11, 3.12, 3.13.

Since coordinode-embedded now uses abi3-py311 wheels (compatible with 3.11+), CI should validate that the SDK itself runs correctly on 3.14.

[coderabbitai]

🔗 Related PRs

#58 - fix(ci): set PYO3_CROSS_PYTHON_VERSION for aarch64 Linux cross-compilation [merged]

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