feat(stream): Add `AsciiChar`

[epage]

This can be used like u8 or char but its guaranteed to work with both byte streams and &str streams.

A A! macro is introduced to provide a "literal" form of this for easier creation. An invalid value is a compiler error.

The goal is to resolve issues where we could end up splitting on non-UTF8 characters because we allow bytes to be used with &str but we need something that can work with both.

[coveralls]

Pull Request Test Coverage Report for Build 7817064688

• -89 of 95 (6.32%) changed or added relevant lines in 3 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-1.1%) to 41.585%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/parser.rs	0	2	0.0%
src/stream/ascii.rs	5	14	35.71%
src/stream/mod.rs	1	79	1.27%
<!--	Total:	6	95	6.32%	-->

Files with Coverage Reduction	New Missed Lines	%
src/ascii/mod.rs	2	54.58%
<!--	Total:	2		-->

Totals
Change from base Build 7805587131:	-1.1%
Covered Lines:	1322
Relevant Lines:	3179

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💛 - Coveralls

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 6.31579% with 89 lines in your changes missing coverage. Please review.

Project coverage is 41.58%. Comparing base (40c2e84) to head (65da275). Report is 279 commits behind head on main.

Files with missing lines	Patch %	Lines
src/stream/mod.rs	1.26%	78 Missing :warning:
src/stream/ascii.rs	35.71%	9 Missing :warning:
src/parser.rs	0.00%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #459 +/- ## ========================================== - Coverage 42.67% 41.58% -1.09% ========================================== Files 18 19 +1 Lines 3084 3179 +95 ========================================== + Hits 1316 1322 +6 - Misses 1768 1857 +89 ```

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