It seems `_ERR_MSG` was silently removed in Python 3.14, leading to an
`ImportError` when running the extractor.
To fix this, we explicitly set `_ERR_MSG` when the existing import fails
(using `_ERR_MSG_PREFIX` which is available in Python 3.14+, along with
the bits that make up the difference between this and `_ERR_MSG`).
Does a bunch of things, unfortunately all in the same place, so my
apologies in advance for a slightly complicated commit.
As for the changes themselves, this commit
- Adds timers for the old and new parsers. This means we get the overall
time spent on these parts of the extractor if the extractor is run with
`DEBUG` output shown.
- Adds logging information (at the `DEBUG` level) to show which
invocations of the parsers happen when, and whether they succeed or not.
- Adds support for using an environment variable named
`CODEQL_PYTHON_DISABLE_OLD_PARSER` to disable using the old parser
entirely. This makes it easier to test the new parser in isolation.
- Fixes a bug where we did not check whether a parse with the new parser
had already succeeded, and so would do a superfluous second parse.
