Track architectural improvements: Move code to core package

[coderabbitai[bot]]

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Several TODOs in the codebase indicate planned architectural improvements to move code to a "core" package.

Found in:

• packages/starknet/lib/src/signer/base_signer.dart
• packages/starknet_provider/lib/src/model/function_call.dart

This issue tracks the planned architectural improvements to better organize the codebase by moving appropriate code to a core package.

Related PR: #445