www/py-adblock: Prepare for py-maturin >= 0.13.0

• Since the 0.13.0 release maturin no longer searches for the Python interpreters by default and uses the current interpreter found in the PATH environment variable. Thus set BINARY_ALIAS to give a specific Python interpreter during build.

• Fix build as well if building the port for multiple Python flavors by using FLAVOR_DEFAULT_ALL in poudriere and BUILD_ALL_PYTHON_FLAVORS in the make.conf.

• Add CONFLICTS_INSTALL because a shared library is installed outside of Python's site-lib directory.

• No bump of PORTREVISION as the package content isn't changed.

PR: 266211 (related)
Approved by: portmgr (blanket)