improve calculate_next_block_base_fee doc

[tcoratger]

The calculate_next_block_base_fee function has until now included quite a few formulas and nested logic with little documentation. I thought it might be quite hard to read for a newcomer. So I added several improvements (in my opinion), don't hesitate to tell me if some are not suitable:

• I added a slightly more extensive comment doc at the start of the function to briefly explain what it does and the link with EIP-1559.
• I divided if / else if / else into three with documentation each time to understand the logic related to the gas_target.
• In each statement, I refactored the operations a little to be able to read them as a single operation and I favored multiplication rather than two successive divisions (normally in terms of performance it goes a little faster if I'm not mistaken, so it's always winning even if it's very minor).

[codecov]

Codecov Report

Merging #5135 (5ad06e5) into main (a6bee72) will decrease coverage by 0.12%.
Report is 13 commits behind head on main.
The diff coverage is 93.33%.

Files	Coverage Δ
crates/primitives/src/basefee.rs	98.11% <93.33%> (-0.07%)	⬇️

... and 32 files with indirect coverage changes

Flag	Coverage Δ
integration-tests	17.07% <0.00%> (-0.02%)	⬇️
unit-tests	62.13% <93.33%> (-0.11%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
reth binary	30.85% <ø> (ø)
blockchain tree	80.82% <ø> (ø)
pipeline	88.36% <ø> (ø)
storage (db)	74.60% <ø> (ø)
trie	95.00% <ø> (+0.06%)	⬆️
txpool	55.31% <ø> (-0.03%)	⬇️
networking	78.16% <ø> (-0.03%)	⬇️
rpc	57.80% <ø> (-0.69%)	⬇️
consensus	63.01% <ø> (ø)
revm	24.47% <ø> (+0.28%)	⬆️
payload builder	7.95% <ø> (ø)
primitives	84.72% <93.33%> (-0.12%)	⬇️

[mattsse]

lgtm, pending @Rjected

[Rjected]

LGTM, I like the docs a lot, the basefee method looks equivalent