[Phase 3] Extrinsic Codec Refactoring (Issue #39)

[gmajor-encrypt]

Summary

This PR refactors the Extrinsic transaction encoder/decoder for the SCALE codec library.

Features Implemented

Extrinsic v4 Format Support

• Signed extrinsics: Version byte with 0x80 flag
• Unsigned extrinsics: Version byte without 0x80 flag
• Length prefix: Compact-encoded length

Components

Signature (class)

• Signer address
• Signature bytes (64 bytes for Sr25519/Ed25519, 65 for Ecdsa)
• Extra data (era, nonce, tip)
• Signature type detection

Extrinsic (class)

• Call data (pallet, function, args)
• Optional signature
• Extra data
• Convenience getters

ExtrinsicBuilder (class)

• Fluent builder pattern
• pallet() / function() setters
• args() / arg() for arguments
• signer() / signature() for signing
• nonce() / tip() for extra data
• immortal() / mortal() for era
• build() / buildUnsigned()

ExtrinsicEncoder (class)

• SCALE encoding for extrinsics
• MultiAddress encoding (Id variant)
• Signature encoding
• Era encoding (immortal/mortal)
• Compact-encoded nonce/tip

ExtrinsicDecoder (class)

• SCALE decoding for extrinsics
• MultiAddress decoding
• Signature decoding
• Extra data decoding
• Call data extraction

Example Usage

use Substrate\ScaleCodec\Extrinsic\{ExtrinsicBuilder, ExtrinsicEncoder, ExtrinsicDecoder};

// Build unsigned extrinsic
$unsigned = ExtrinsicBuilder::create()
    ->pallet('System')
    ->function('remark')
    ->palletIndex(0)
    ->functionIndex(0)
    ->buildUnsigned();

// Build signed extrinsic
$signed = ExtrinsicBuilder::create()
    ->pallet('Balances')
    ->function('transfer')
    ->palletIndex(5)
    ->functionIndex(0)
    ->signer($signerAddress)
    ->signature($signature)
    ->nonce(1)
    ->tip(0)
    ->mortal(64, 100)
    ->build();

// Encode
$encoder = new ExtrinsicEncoder();
$encoded = $encoder->encode($signed);

// Decode
$decoder = new ExtrinsicDecoder();
$decoded = $decoder->decode($encoded);

Tests

• Unit tests in tests/Extrinsic/ExtrinsicTest.php
• Signature tests
• Extrinsic tests
• Builder tests
• Encoder/decoder tests

Issue

• Closes [Phase 3] Extrinsic Codec Refactoring #39

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Ready for review.