Introduce ECDSAKey and decouple from ethgo lib transactions signing logic

[Stefan-Ethernal]

Description

The PR introduces ECDSAKey which is used to encapsulate ECDSA private, public key and Ethereum address. As a consequence, transaction signing logic needed to be changed to rely on crypto.Key instead of ethgo.Key interface and instead of the ethgo abstraction for Transaction and transaction signers, the abstractions from the Blade are used.

Changes include

• Bugfix (non-breaking change that solves an issue)
• Hotfix (change that solves an urgent issue, and requires immediate attention)
• New feature (non-breaking change that adds functionality)
• Breaking change (change that is not backwards-compatible and/or changes current functionality)

Breaking changes

Please complete this section if any breaking changes have been made, otherwise delete it

Checklist

• I have assigned this PR to myself
• I have added at least 1 reviewer
• I have added the relevant labels
• I have updated the official documentation
• I have added sufficient documentation in code

Testing

• I have tested this code with the official test suite
• I have tested this code manually

Manual tests

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Documentation update

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Additional comments

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