Allow input to take a specified number of characters

[merelymyself]

Description

Title; fixes #9208.

User-Facing Changes

input now can specify a certain number of characters to read.

Tests + Formatting

No CI tests; can't find a way to implement.

~/CodingProjects/nushell> let user_input = (input --numchar 2)                                           
~/CodingProjects/nushell> echo $user_input                                                        
te

After Submitting

[codecov]

Codecov Report

Merging #9242 (987a872) into main (ca275f5) will decrease coverage by 0.03%.
The diff coverage is 41.86%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9242      +/-   ##
==========================================
- Coverage   68.54%   68.52%   -0.03%     
==========================================
  Files         636      636              
  Lines      102281   102319      +38     
==========================================
- Hits        70110    70109       -1     
- Misses      32171    32210      +39     

Impacted Files	Coverage Δ
crates/nu-command/src/platform/input/input_.rs	29.37% <41.86%> (+1.32%)	⬆️

... and 4 files with indirect coverage changes

[fdncred]

Very nice. People have been asking for this.

[fdncred]

Thanks. I think it looks pretty good.

I was nitpicking your numchar parsing thinking this may be better

        let numchar = match numchar {
            Some(numchar) => numchar,
            None => Spanned {
                item: i64::MAX,
                span: call.head,
            },
        };

but it's doing the same thing anyway. So, it's no big deal.