fix parse_calls negative number detection - #18514

Description

Makes the negative number or short flag detection work with OneOff when the options can be negative numbers, necessary for the tests on #18511 to pass.

User-facing changes (Release notes)

Fixed negative arguments for oneof parameters

Parameters with int, float and number types can be supplied negative arguments:

def foo [p: int] {
    $p
}

foo -2
# => -2

However this didn't work with parameters with types like oneof<int, ...>:

def foo [p: <int, string>] {
    $p
}

foo -2
# => Error: nu::parser::unknown_flag
# => 
# =>   × The `foo` command doesn't have flag `-2`.
# =>    ╭─[repl_entry #1:3:6]
# =>  2 │ 
# =>  3 │ foo -2
# =>    ·      ┬
# =>    ·      ╰── unknown flag
# =>    ╰────
# =>   help: Use `--help` to see available flags

This is now fixed:

def foo [p: <int, string>] {
    $p
}

foo -2
# => -2

Additional notes

N/A