Validate compose fee parameters

[caydyan]

Supersedes #3381 with the same fix rebased onto the current develop branch.

prepare_fee_parameters() accepted negative fee inputs. Negative exact_fee, sat_per_vbyte, or max_fee can flow into input selection and change calculation, producing impossible negative-fee compose results or change outputs larger than the selected inputs.

This PR rejects negative compose fee parameters up front with a clear ComposeError.

Changes:

• Rejects negative exact_fee.
• Rejects negative sat_per_vbyte.
• Rejects negative max_fee.
• Adds regression coverage for all three fee parameters.

Tests:

• python -m pytest counterpartycore/test/units/api/composer_test.py::test_prepare_fee_parameters -q
• python -m pytest counterpartycore/test/units/api/composer_test.py -q
• python -m ruff check counterpartycore/lib/api/composer.py counterpartycore/test/units/api/composer_test.py
• python -m ruff format --check counterpartycore/lib/api/composer.py counterpartycore/test/units/api/composer_test.py
• git diff --check

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