fix: ForeignKey<Self> doesn't compileFix self foreignkey

[eibrahim95]

In database models, if you used ForeignKey<Self> you'd get an error as described by #298

In this PR, I added a check in the symbol resolver to check for any generic Self and replace it with the struct name.
This also affects migration generation which now references Self with full struct crate name.

[codecov]

Codecov Report

Attention: Patch coverage is 98.14815% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
cot-codegen/src/symbol_resolver.rs	97.22%	0 Missing and 1 partial ⚠️

Flag	Coverage Δ
rust	88.02% <98.14%> (+0.02%)	⬆️

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Files with missing lines	Coverage Δ
cot-codegen/src/model.rs	92.27% <100.00%> (+0.05%)	⬆️
cot-macros/src/model.rs	92.79% <100.00%> (+0.26%)	⬆️
cot-codegen/src/symbol_resolver.rs	97.37% <97.22%> (+0.18%)	⬆️

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[m4tx]

Sorry for my delay in reviewing this. Looks good; thanks a lot for the contribution!