Handle exponents on the lexer side, treat them as integer

[ghaith]

Treat the exponents as part of the integer.
Add tests using E1.. as an identifier
Add support for exponents without the 0

[codecov]

Codecov Report

Merging #263 (0cd772f) into master (3d61764) will decrease coverage by 0.01%.
The diff coverage is 80.00%.

@@            Coverage Diff             @@
##           master     #263      +/-   ##
==========================================
- Coverage   94.90%   94.89%   -0.02%     
==========================================
  Files          42       42              
  Lines       11169    11184      +15     
==========================================
+ Hits        10600    10613      +13     
- Misses        569      571       +2     

Impacted Files	Coverage Δ
src/parser/expressions_parser.rs	96.18% <80.00%> (-0.76%)	⬇️
src/ast.rs	90.08% <0.00%> (+0.16%)	⬆️
src/typesystem.rs	96.97% <0.00%> (+0.25%)	⬆️
src/validation.rs	80.97% <0.00%> (+0.54%)	⬆️

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