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

Previously we would check if the tag is special to validate that it isn't
reserved, and then to actually get the test case properties. We also did
the first check in particularly terrible order, leading to a lot of wasted
work.

The new implementation does property extraction while checking validity,
and is structured to avoid as much work as possible by early checks.

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.

Similar to the change that removed `std::set` from the test registration
path, this saves an allocation per test to run, and is faster to boot.

Technically, the performance of selecting tests for multiple OR-joined
filters, each of which selects many (most) tests is a bit slower,
but that is not very common use case.

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).