feat(layers): FillTxLayer

[yash-atreya]

Motivation

Unify the ManagedNonceProvider and GasEstimatorProvider to concurrently populate missing tx fields.

Solution

Implement a FillTxLayer that concurrently calls the following methods:

• get_next_nonce from ManagedNonceProvider to populate the nonce field.
• handle_eip1559_tx and handle_legacy_tx from GasEstimatorProvider to populate gas related fields.
• get_chain_id from provider directly to populate the chain_id field.

In order to achieve this, the following changes were made:

1. Introduced the Clone trait bound on the Provider<N, T> for ProviderBuilder enable the cloning of the underlying provider and initializing of the ManageNonceProvider and GasEstimatorProvider directly in FillTxLayer

2. Added pub(crate) fn new method to both ManageNonceProvider and GasEstimatorProvider to instantiate them directly from the FillTxLayer

PR Checklist

• Added Tests
• Added Documentation
• Breaking changes

[prestwich]

closing in favor of #426