Add GST sentence parser

[zhrbrk]

#54 Add GST sentence parser with unit test.
GST is now a stand-alone feature, and also added into the GNSS features package.

[elpiel]

Thank you very much for the PR!
I have a few comments on the doc comments.
Can you also make sure you use /// doc comments instead of regular // comments for the struct?

I will give it a more thorough look sometime later this week, in the meantime I will run the CI.

[elpiel]

Suggested change

	// 1 2 3 4 5 6 7 8 9
	// | | | | | | | | |
	// $ --GST,hhmmss.ss,x,x,x,x,x,x,x*hh<CR><LF>
	/// ```text
	/// 1 2 3 4 5 6 7 8 9
	/// | | | | | | | | |
	/// $ --GST,hhmmss.ss,x,x,x,x,x,x,x*hh<CR><LF>
	/// ```

[elpiel]

Suggested change

	// Example: $GPGST,182141.000,15.5,15.3,7.2,21.8,0.9,0.5,0.8*54
	/// Example: `$GPGST,182141.000,15.5,15.3,7.2,21.8,0.9,0.5,0.8*54`

[codecov]

Codecov Report

Attention: Patch coverage is 85.18519% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 77.78%. Comparing base (af2edeb) to head (b15db1c).
Report is 1 commits behind head on main.

❗ Current head b15db1c differs from pull request most recent head 61f33ee. Consider uploading reports for the commit 61f33ee to get more accurate results

Files	Patch %	Lines
src/sentences/gst.rs	87.50%	3 Missing ⚠️
src/parser.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #121      +/-   ##
==========================================
+ Coverage   77.62%   77.78%   +0.16%     
==========================================
  Files          34       35       +1     
  Lines        1247     1274      +27     
==========================================
+ Hits          968      991      +23     
- Misses        279      283       +4     

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