Defined types visit support

[ERoydev]

What

Improved extractFieldsFromTypeManifest to capture baseType, nesting, and optional for fields.

• Handles lists, fixed-length arrays, and optional types accurately.
• Adds detection for struct types to differentiate between primitives and user-defined structs.
• Find the baseType of the element if it is inside a nested structure

Updated getTypeManifestVisitor to:

• Correctly generate Dart classes for structs, enums, and tuple/struct variants.
• Support optional fields (Type?) and nested structs.
• Map Rust number types to Dart types (int, BigInt) correctly.

Consistently use snake_case for file names and PascalCase for class/type names in Dart.

• Ensured the RenderMap visitor passes all required context for accounts, types, instructions, and PDAs.

Note: In the next PR i will apply typization and fix all eslint errors

Add appropriate imports for typed arrays, Solana types, and shared utilities.

Dependent PR

#2