Three misspellings in comments: "reuired" -> "required",
"ambigous" -> "ambiguous", "neccessarily" -> "necessarily".

Per docs/contributing.md, the amalgamated files under extras/ are left
untouched even though they carry the same typos.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

The new implementation keeps track of found escape codes in a separate
vector, which has two advantages:
1) The handling of inputs without any escape codes is much faster. As
   this will be the case for majority of inputs, this should provide
   nice speedup all around.
2) We no longer mangle unrelated 0xFFs in the user-provided input.

Closes #3199

The old implementation always forced copy (and likely alloc) for
each input when matching it. The new implementation uses the
case-insensitive comparators to avoid all that.

This provides interesting performance improvement for selecting
individual test, doing something like `./tests/SelfTest "ABC*"`
is almost 10% faster.

We generally do not even try to pretend to support more than plain ASCII,
because doing unicode in old C++ standards is a pain and a half. For
`toLower`, we used to wrap `std::tolower` with multiple casts to avoid UB,
but calling into it is relatively slow, and it tries to handle different
locales, which could cause unexpected results.

In addition, the new implementation is significantly faster, which helps
speed up the initial process bring up (as comparing tags, and thus test
cases is now faster).

This is _technically_ a performance improvement, but in actuality
it is a tiny cleanup so it stops bothering me.

By avoiding `std::set`, we save 1 allocation per checked test case,
and the sort + pairwise check has much nicer cache behaviour, leading
to much faster check.

Overall, the check is only a tiny part of the startup overhead, but
the improvement is large enough that it ends up measurable in binaries
with many tests (e.g. `SelfTest`).

This provides minor compile-time optimization.

GCC is especially bad, as it had quadratic scaling in the number of
registered test cases in a TU, but Clang also scaled superlinearly, and
this commit fixes both.

AIUI:
1) Each `TEST_CASE` creates a separate global fragment to handle creating
   the `unique_ptr<ITestInvoker>`, moving the instance into AutoReg,
   destroying the old instance, etc, etc.
2) With optimizations enabled, the compiler merges all these global
   fragments into one big global fragment.
3) Then the compiler runs various optimizations passes on this new global
   fragment.
4) Because some of the passes scale superlinearly, the compilation times
   scale superlinearly in the number of `TEST_CASE` in a translation unit.

For bonus point, no optimization actually happens.

This commit fixes the problem (for non-LTO builds) by adding new `AutoReg`
constructor, one that takes the function pointer raw, instead of wrapped
in `ITestInvoker`. By delaying the construction of the `ITestInvoker`
into the outlined constructor, we no longer create big global fragments
for the compiler to optimize.

This provides further speed-ups for TUs with many test cases templated
over the same set of types. For especially test-heavy (but still
realistic) TUs, the speed up is up to 20%.