Implement local variables

[sidrasali]

Added support for local variable declaration and assignments.

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Closes #24

[github-actions]

Code Coverage

File	Coverage [91.53%]	✅
src/jsMain/kotlin/exceptions/CompilationExceptions.kt	55.26%	❌
src/jsMain/kotlin/lexer/Lexer.kt	96.23%	✅
src/jsMain/kotlin/parser/ASTNode.kt	100.00%	✅
src/jsMain/kotlin/parser/BlockItems.kt	100.00%	✅
src/jsMain/kotlin/parser/Expressions.kt	100.00%	✅
src/jsMain/kotlin/parser/Functions.kt	100.00%	✅
src/jsMain/kotlin/parser/Parser.kt	96.80%	✅
src/jsMain/kotlin/parser/Programs.kt	100.00%	✅
src/jsMain/kotlin/tacky/Instructions.kt	85.42%	✅
src/jsMain/kotlin/tacky/TackyGenVisitor.kt	92.31%	✅

Total Project Coverage	91.30%	✅