GH-101362: Optimise pathlib by deferring path normalisation by barneygale · Pull Request #101560 · python/cpython

`PurePath` now normalises and splits paths only when necessary, e.g. when
`.name` or `.parent` is accessed. The result is cached. This speeds up path
object construction by around 4x.

`PurePath.__fspath__()` now returns an unnormalised path, which should be
transparent to filesystem APIs (else pathlib's normalisation is broken!).
This extends the earlier performance improvement to most impure `Path`
methods, and also speeds up pickling, `p.joinpath('bar')` and `p / 'bar'`.

This also fixes pythonGH-76846 and pythonGH-85281 by unifying path constructors and
adding an `__init__()` method.