update grammar rules for assignment and cast expressions

Refined `AssignmentExpression` grammar to include optional "Operator"
and updated `CastExpression` to support dynamic `TypeValue`.

Added validation to throw `ParserException` when no `:` or `=` follows
an argument name

… parameter

simplify expression parsing logic

Allow end call expr list with comma

replace `LeftHandSideExpression` with `MemberExpression` in
`AssignmentExpression` and related grammar adjustments

simplify declaration parsing logic

Replaced `AddToDeclaration` with `DeclarationAssignmentExpression`

Prohibited undefined vars like `let x` grammar-wise

- Replaced null returns with `ParserException` for better error handling
- Extracted `CurrentIsStatement` for cleaner parsing logic
- Updated grammar to improve clarity on `MemberExpression`

Closes #233

Specify value of expected tokens for certain types

- Updated `TokenTypes` to separate `Assign` and `Operator` patterns,
improving token categorization.
- Added `Distinct()` to `TokenTypesProvider` for unique token handling.
- Adjusted `GeneratedRegexContainer` to include `ExplicitCapture` for
better regex performance.

Closes #233

Standardized null safety for parent scopes across AST nodes, replacing direct access with conditional checks and fallback to `Scope.Empty`.

Desugar Compound Assignment

Closes #233

Closes #233

Leave Expression the only cloning nodes