refactor: decode_legacy_tx for consistency with typed transactions

[ooochoche]

Refactor

Refactor decode_legacy_tx for consistency with typed transactions

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Build-related changes
• Documentation content changes
• Other (please describe):

The function has been splitted into two steps

• Step 1: Decodes encoded_tx_data and returns the decoded data.
• Step 2: Implements a trait in crates/utils/src/eth_transaction/transaction.cairo to decode transaction fields.

Resolves: #979

Refactor

• Decodes transaction
• Trait to decode transaction fields
• Consistency with typed transactions eip2930.cairo

Does this introduce a breaking change?

• Yes
• No

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This change is 

[enitrat]

can you format?