Rename the compilation result from script to bytecode

[someone235]

Closes #165

Use bytecode consistently for SilverScript compiler output, while retaining established transaction terms such as signature scripts, redeem scripts, and script public keys.

This is a breaking terminology change for SilverScript source, serialized compiler artifacts, and the Rust API.

Language Behavior Changes

• Rename the compile-time expressions this.scriptSize and this.scriptSizeDataPrefix:

entry main(int expectedSize, byte[] expectedPrefix) {
    require(expectedSize == this.bytecodeSize);
    require(expectedPrefix == this.bytecodeSizeDataPrefix);
}

• Rename the compiled artifact’s JSON field from script to bytecode:

{
  "contract_name": "Example",
  "bytecode": [81]
}

• Rename CompiledContract::script to CompiledContract::bytecode for programmatic compiler consumers:

let compiled = compile_contract(source, &args, options)?;
println!("Bytecode length: {}", compiled.bytecode.len());

• Update debugger output and APIs to describe execution in terms of compiled bytecode.