CASSANDRA-20997: Support Python 3.12 and 3.13 in cqlsh

[arvindKandpal-ksolves]

Support Python 3.12 and 3.13 in cqlsh by vendoring the pyasyncore package.

Context / Background

Currently, starting cqlsh with Python 3.12 or 3.13 fails. Even if the version guards are relaxed, it crashes with a DependencyException because Python 3.12 removed the asyncore module from the standard library (PEP 594). The bundled Datastax python driver (cassandra-driver-internal-only) relies on asyncore as a default fallback event loop when C-extensions (libev) are not present, causing it to crash at import time.

Changes Made

To fix this without modifying the bundled third-party driver's internal code:

1. Dependency Management: Updated .build/build-resolver.xml to fetch the official pyasyncore package from PyPI and package it as a .zip in the lib/ directory.
2. Path Injection: Added 'pyasyncore-' to the third_parties tuple in bin/cqlsh.py so it gets injected into sys.path at runtime (matching the existing approach for wcwidth and pure_sasl).
3. Version Guards: Relaxed the supported version checks in both bin/cqlsh and bin/cqlsh.py to allow Python up to 3.13.

Testing

• Successfully ran ant cqlsh to verify that pyasyncore-1.0.5-py3-none-any.zip is downloaded and copied to the lib/ directory.
• Tested cqlsh locally with CQLSH_PYTHON=python3.12 and CQLSH_PYTHON=python3.13 to confirm it successfully connects to the cluster without throwing driver import errors.
• Confirmed that Python 3.14 correctly triggers the "unsupported version" warning message.

patch by Arvind Kandpal; for CASSANDRA-20997