Enhance strip_trailing_separator to handle UNC and extended-length paths on Windows #1192

Job	Run time
Tests in Containers (ci-jupyter-container, ubuntu-latest, mcr.microsoft.com/devcontainers/univers...	3m 56s
Builds (macos-latest, x86_64-apple-darwin, yes)	2m 52s
Tests (macos-latest, x86_64-apple-darwin, yes)	12m 25s
Tests (windows-latest, x86_64-pc-windows-msvc, yes)	7m 8s
Builds (macos-14, aarch64-apple-darwin, yes)	2m 43s
Tests in Containers (ci-homebrew-container, ubuntu-latest, homebrew/brew, x86_64-unknown-linux-musl)	3m 25s
Builds (windows-latest, aarch64-pc-windows-msvc)	5m 11s
Tests (macos-14, aarch64-apple-darwin, yes)	12m 32s
Builds (windows-latest, x86_64-pc-windows-msvc)	3m 46s
Env Tests (ci-poetry-global, windows-latest, x86_64-pc-windows-msvc)	5m 19s
Tests (ubuntu-latest, x86_64-unknown-linux-musl, yes)	8m 55s
Builds (ubuntu-latest, x86_64-unknown-linux-musl, yes)	1m 59s
Env Tests (ci-poetry-global, ubuntu-latest, x86_64-unknown-linux-musl)	2m 28s
Env Tests (ci-poetry-project, windows-latest, x86_64-pc-windows-msvc)	5m 0s
Env Tests (ci-poetry-custom, windows-latest, x86_64-pc-windows-msvc)	5m 38s
Env Tests (ci-poetry-custom, ubuntu-latest, x86_64-unknown-linux-musl)	2m 33s
Env Tests (ci-poetry-project, ubuntu-latest, x86_64-unknown-linux-musl)	2m 35s
	1h 28m 25s

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