fix: name the function and add a span to unknown-named-argument errors

[prql-bot]

Passing a named argument that no parameter matches produced an error with no span and a Debug-printed ident. From the snapshot #6136 added yesterday:

Error: unknown named argument `b` to closure Some(["std", "not"])

Two fixes, in apply_args_to_closure and at its call site in the resolver:

• Use closure.as_debug_name() instead of {:?} on name_hint, matching the phrasing of the sibling arity error a few lines above (Too many arguments to function \not``).
• Attach the call-site span via with_span_fallback, so the error renders with the usual ariadne caret instead of a bare one-liner. with_span_fallback rather than with_span, so a span set deeper in the error isn't clobbered.

Same input now reads:

Error:
   ╭─[ :1:18 ]
   │
 1 │ from x | select (std.not {a} b:1)
   │                  ───────┬───────
   │                         ╰───────── unknown named argument `b` to function `not`
───╯

bad_error_messages::not_with_named_arg — added in #6136, which flagged exactly this ("the message has no span and Debug-prints the ident") — moves to error_messages::unknown_named_arg with updated snapshots, plus a third case (from x | take 1 b:2) so the coverage isn't all std.not.

Found during the nightly survey of semantic/resolver/functions.rs.