fix(nushell): adapt the completer to the 0.116 contract (#4934)

* fix(nushell): adapt the completer to the 0.116 contract

Nushell 0.116 runs an external completer on a background worker
without the terminal unless the registered closure reaches a
command carrying the @interactive attribute. Interactivity is
seen through the closure to the command it calls, so wrap the
completion logic in an @interactive entry point and register a
closure that ends with the call to it.

Read the named `place` input instead of the deprecated
positional `spans`; $place.command carries the same token list.

An @interactive completer cannot decline with null (null reads
as a dismissed picker), so request the fallback explicitly when
the `**` trigger is absent, keeping plain file completion
working. The previous external completer is still called when
the trigger is absent.

The script now requires Nushell 0.116+, since @interactive is a
parse error on older versions.

Fixes #4932

* fix(nushell): retry the previous completer with the legacy spans input

The fallback to the previously configured external completer always
handed it the new `place` input. A completer that still declares the
legacy `spans` parameter errors on a record, so the fallback silently
produced no completions for pre-0.116 completers (e.g. older Carapace
installs).

Try `place` first, then retry with the token list, which is what the
old positional bridge handed such completers.

* docs(nushell): note the 0.116 requirement and load order

Requires Nushell 0.116.1+, where a completion can take the terminal
through the @interactive attribute, and the wrapper captures the
external completer present at load time.

CHANGELOG.md

@@ -5,6 +5,8 @@ CHANGELOG
 ------
 - Fixed `--with-shell` on Windows not detecting cmd, PowerShell, and pwsh, which made fzf quote commands and entries for a POSIX shell (#4936) (@vimkim)
     - e.g. With `--with-shell "cmd.exe /d /c"`, `--preview '"C:\Program Files\nu\bin\nu.exe" --version'` failed
+- nushell
+    - The completion integration now requires nushell 0.116.1 or above, where an interactive completer can take the terminal through the `@interactive` attribute (#4934) (@sim590)
 
 0.74.5
 ------