preprocessor: detect circular includes

[BrettMayson]

Fixes #914

I can see some rare cases where this is allowed with #if and other checks, but I think that's rare enough that this PR is fine instead of crashing

[codecov]

Codecov Report

Attention: Patch coverage is 96.42857% with 2 lines in your changes missing coverage. Please review.

Project coverage is 67.5%. Comparing base (7eadf0f) to head (fc5e970).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
...bs/preprocessor/src/codes/pe29_circular_include.rs	97.5%	1 Missing ⚠️
libs/preprocessor/src/processor/directives.rs	85.7%	1 Missing ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
libs/preprocessor/src/processor/mod.rs	89.7% <100.0%> (+0.3%)	⬆️
...bs/preprocessor/src/codes/pe29_circular_include.rs	97.5% <97.5%> (ø)
libs/preprocessor/src/processor/directives.rs	91.2% <85.7%> (-0.1%)	⬇️

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