Validate v2 API boolean parameters

[caydyan]

Summary

This validates v2 API boolean query parameters instead of silently coercing unsupported values to false.

Currently, prepare_args() parses booleans with str_arg.lower() in ["true", "1"], so any unsupported value becomes False. For example:

• /v2/transactions?show_unconfirmed=maybe returns 200 OK
• /v2/transactions?verbose=maybe is accepted and treated as non-verbose

The fix accepts only true, 1, false, and 0 for boolean route arguments and returns the existing 400 API error path for unsupported values. It also validates the shared non-compose verbose query parameter before executing the route.

Tests

• .venv/bin/pytest counterpartycore/test/units/api/apiserver_test.py::test_invalid_bool_param_rejected -q
• .venv/bin/pytest counterpartycore/test/units/api/apiserver_test.py -q
• .venv/bin/ruff check counterpartycore/lib/api/apiserver.py counterpartycore/test/units/api/apiserver_test.py
• .venv/bin/ruff format --check counterpartycore/lib/api/apiserver.py counterpartycore/test/units/api/apiserver_test.py
• git diff --check

If this qualifies for the project bounty program, BTC payout address:
bc1qev5ant33v5y89qqjvcf4mh9hlax5svqf5xd7gc

[caydyan]

Closing this master-based PR in favor of the develop-based replacement #3420: #3420