feat: add constructor macro and unify contract/storage derives

[d1r1]

Summary

Introduces #[constructor] macro for contract initialization and unifies Contract/Storage implementation to reduce code duplication.

Changes

New Features

• #[constructor] macro for defining contract initialization separately from runtime methods
• Supports trait implementations where constructor can't be part of the trait

Bug Fixes

• Fixed undefined variable errors in deploy method generation
• Removed unnecessary function_id imports from generated code

Refactoring

• Unified Contract and Storage derives to share same implementation
• Extracted common deploy logic to ParsedMethod::generate_deploy_body()
• Removed redundant Contract implementation

Usage

// Separate initialization from trait implementation
#[constructor(mode = "solidity")]
impl<SDK> Token<SDK> {
    pub fn constructor(&mut self, supply: U256) { }
}

#[router(mode = "solidity")]
impl<SDK> TokenInterface for Token<SDK> {
    fn transfer(&mut self, to: Address, amount: U256) -> bool { }
}

Breaking Changes

• Internal Contract derive implementation changed (API remains compatible)