[BUG]: A distribution without a version, such as java@tem, fails with a Lua error #98

Version
vfox-java main (3b38e44) and v0.6.1, vfox 1.0.13

OS
Linux

Describe the bug
A version that names only the distribution stops the plugin with a Lua error. vfox install java@tem and vfox install java@temurin fail in PreInstall, and vfox use --global java@tem fails in PreUse:

$ vfox install java@tem
plugin [PreInstall] method error: ~/.vfox/plugin/java/lib/distribution_version.lua:79: attempt to index a non-table object(nil) with key 'match'
stack traceback:
	~/.vfox/plugin/java/lib/distribution_version.lua:79: in function 'convert_version_for_api'
	~/.vfox/plugin/java/lib/distribution_version.lua:134: in function 'parse_version'
	~/.vfox/plugin/java/hooks/pre_install.lua:29: in main chunk
	[G]: ?
failed to install java
$ vfox use --global java@tem
plugin [preUse] error: err:~/.vfox/plugin/java/lib/distribution_version.lua:79: attempt to index a non-table object(nil) with key 'match'
stack traceback:
	~/.vfox/plugin/java/lib/distribution_version.lua:79: in function 'convert_version_for_api'
	~/.vfox/plugin/java/lib/distribution_version.lua:134: in function 'parse_version'
	~/.vfox/plugin/java/hooks/pre_use.lua:20: in main chunk
	[G]: ?

A .sdkmanrc holding java=tem selects nothing, even with 21.0.8+9-tem installed. ParseLegacyFile raises the same error there, and vfox env -s bash exits 0 without printing it. The v0.6.1 release zip fails the same way, at lines 66 and 121 of lib/distribution_version.lua.

When the name has no version part, parse_version takes it as the distribution and leaves version nil:

It then hands that nil to convert_version_for_api, added in #57, which calls version:match:

Skipping the conversion when there is no version does not fix vfox install. With that change PreInstall fails the same way at lib/foojay.lua:77, which also expects a version:

So java@tem needs either an error that asks for a version or a defined meaning, such as the newest release of that distribution.

Found while working on #91.