mode, because "Server" mode does not supply any actual VFS data).

## "Server"
### Description

The "Server" mode is a single in-process handler for "`//xvfs:/`" and additional clients
can call `Xvfs_Register()` to register their filesystem with that handler.  This has the
advantage of being more efficient since there are not one `Tcl_Filesystem` per extension
advantage of being more efficient since there is not one `Tcl_Filesystem` per extension, which have to all be searched through, but instead a single handler which uses a
which have to all be searched through but instead a single handler which uses a
`Tcl_HashTable` to map the namespace to things which have called `Xvfs_Register()`.

The "Server" mode thus has 2 symbols:

  1. `Xvfs_Init()` which initializes the `Tcl_Filesystem` for all of "`//xvfs:/`" as well as setup the empty `Tcl_HashTable`
  2. `Xvfs_Register()` which is for other extensions to call to register their name under "`//xvfs:/`"