Support custom_inputs compose alias

[caydyan]

Addresses #2186.

This is a develop-based replacement for #3368.

Summary:

• Accept custom_inputs as a deprecated compose construct parameter.
• Map custom_inputs to inputs_set, matching the documented behavior users were looking for.
• Keep explicit inputs_set precedence when both are supplied.
• Return a deprecation warning for custom_inputs.

Tests:

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

BTC payout address if this qualifies for a contributor/security reward: bc1qev5ant33v5y89qqjvcf4mh9hlax5svqf5xd7gc