Remove python-like string multiplication (#10293)

# Description
Currently we support "multiplication" of strings, resulting in a terse
way to repeat a particular string.
This can have unintended side effects when dealing with mixed data (e.g.
after parsing data that is not all numbers).
Furthermore as we frequently fall-back to strings while parsing source
code, this introduced a runaway edge case in const evaluation (#10212)

Work for #10233

## Details
- Remove python-like string multiplication.
- Workaround for indentation
  - This should probably be addressed with a purpose built command
- Remove special const-eval error test

# User-Facing Changes
**Major breaking change!**
`"string" * 42` will stop working. (This was used for example in the
stdlib)

We should bless a good alternative before landing this

---------

Co-authored-by: JT <547158+jntrnr@users.noreply.github.com>

crates/nu-std/std/testing.nu

@@ -134,7 +134,7 @@ def show-pretty-test [indent: int = 4] {
     let test = $in
 
     [
-        (" " * $indent)
+        (1..$indent | map {" "} | str join)
         (match $test.result {
             "pass" => { ansi green },
             "skip" => { ansi yellow },