Track version-fox/vfox#745: .nvmrc and .node-version are not applied after a cd #46

.nvmrc and .node-version are not applied when you cd into their directory from a running shell, and a shell that started in such a directory does not go back to the global release when you cd out of it. The cause is in vfox, not in this plugin: vfox env serves the output it cached for the previous directory, and the cache does not know about version files. It is reported upstream as version-fox/vfox#745. This issue tracks it until a vfox release fixes it.

Where it stands

A .vfox.toml is applied in the first, second and last of these. The workaround of #44 is util.forget_env_state: it removes vfox's env-state.json whenever vfox asks the plugin to read a version file, so vfox calculates again at every prompt in such a directory. It cannot help on the way out, because the plugin is not called in a directory with nothing to read.

When vfox has fixed it

• A vfox release contains the fix ([BUG]: vfox env serves the cached output after a cd: a .nvmrc / .node-version is ignored on the way in and kept on the way out vfox#745 and the pull request that closes it). Release: ________
• Replay it with that release, with plugin 0.5.3 and with the plugin of main: the shell of "Several projects in one shell" in docs/scenarios.md, then an edit of the file in the directory the shell is in. The reproduction in [BUG]: vfox env serves the cached output after a cd: a .nvmrc / .node-version is ignored on the way in and kept on the way out vfox#745 is the short form.
• If vfox notices version files itself, edits included: remove util.forget_env_state (added by fix: LTS lines from the index, UTF-16/BOM .nvmrc, .nvmrc after a cd; docs: a page of scenarios #44, lib/util.lua), its call in hooks/parse_legacy_file.lua, its tests and the hiding of __VFOX_CURTMPPATH in tests/hooks_test.lua, and the remark in tests/e2e/windows/verify.go. If vfox only keys the cache on the directory, keep it for edits in place.
• Change the documents that describe the limit, in English and Chinese: docs/nvmrc.md ("When the file is read"), docs/scenarios.md ("Several projects in one shell"), docs/development.md ("Legacy files", "Known gaps"), docs/changes.md, docs/troubleshooting.md, README.md and README_CN.md.
• Say from which vfox version this works, and what older ones do.