[Draft] Restructure payouts

[fhenneke]

This draft PR is an attempt at implementing #427. The PR does not change the values of final results (up to rounding of floats). It changes the structure of the code and intermediate representations.

As a first step, it separates the computation of different parts of the accounting into different functions.

    # compute individual components of payments
    solver_info = compute_solver_info(
        reward_target_df,
        service_fee_df,
        config,
    )
    rewards = compute_rewards(
        batch_data,
        quote_rewards_df,
        exchange_rate_native_to_cow,
        config.reward_config,
    )
    protocol_fees = compute_protocol_fees(
        batch_data,
    )
    buffer_accounting = compute_buffer_accounting(batch_data, slippage_df)

Those functions are implemented in separate files

The results of these steps are converted into data frames for solver payments and for protocol and partner fee payments.

    # combine into solver payouts and partner payouts
    solver_payouts = compute_solver_payouts(
        solver_info, rewards, protocol_fees, buffer_accounting
    )
    partner_payouts = compute_partner_fees(batch_data, config.protocol_fee_config)

Additional changes could remove data frames from intermediate results. This would make it easier to have correct types and detect and handle missing data.

The code can be tested to produce the same transfer files as the old code.
Tests have not been adapted yet and are broken due to changes to intermediate results.