Create separate structs for each StmtKind variant

[codecov[bot]]

Codecov Report

Merging #678 (06a82a6) into main (e62ba14) will decrease coverage by 2.00%. Report is 1 commits behind head on main. The diff coverage is 65.10%.

@@            Coverage Diff             @@
##             main     #678      +/-   ##
==========================================
- Coverage   90.65%   88.65%   -2.00%     
==========================================
  Files         106      109       +3     
  Lines       22065    23900    +1835     
==========================================
+ Hits        20003    21189    +1186     
- Misses       2062     2711     +649     

Files Changed	Coverage Δ
crates/escalier_ast/src/class.rs	100.00% <ø> (ø)
crates/escalier_ast/src/expr.rs	97.77% <ø> (ø)
crates/escalier_hm/src/folder.rs	83.98% <0.00%> (-2.71%)	:arrow_down:
crates/escalier_hm/src/types.rs	80.59% <0.00%> (-0.35%)	:arrow_down:
crates/escalier_hm/src/unify.rs	82.63% <0.00%> (-0.35%)	:arrow_down:
crates/escalier_hm/src/util.rs	78.16% <0.00%> (-0.12%)	:arrow_down:
crates/escalier_hm/src/visitor.rs	33.33% <0.00%> (-0.84%)	:arrow_down:
crates/escalier_hm/src/context.rs	97.81% <57.14%> (-2.19%)	:arrow_down:
crates/escalier_codegen/src/d_ts.rs	61.77% <61.77%> (ø)
crates/escalier_codegen/src/js.rs	64.37% <64.37%> (ø)
... and 13 more

... and 5 files with indirect coverage changes