feat: Begin constructing context using bidsschematools types

[effigies]

Builds on bids-standard/bids-specification#2133. Replaces #24.

This is not complete, but should be a good starting point. Apologies for the delay.

[codecov]

Codecov Report

❌ Patch coverage is 66.02564% with 53 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.94%. Comparing base (d9ebe1f) to head (891d403).
⚠️ Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
src/bids_validator/context.py	59.23%	45 Missing and 8 partials ⚠️

❗ There is a different number of reports uploaded between BASE (d9ebe1f) and HEAD (891d403). Click for more details.

HEAD has 19 uploads less than BASE

Flag	BASE (d9ebe1f)	HEAD (891d403)
	38	19

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #26      +/-   ##
==========================================
- Coverage   91.62%   84.94%   -6.68%     
==========================================
  Files          10       12       +2     
  Lines         442      598     +156     
  Branches       65       95      +30     
==========================================
+ Hits          405      508     +103     
- Misses         23       68      +45     
- Partials       14       22       +8     

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