Refactor base fee calculation

[gurukamath]

What was wrong?

1. The base fee calculation should be separated into its own function so that the t8n tool can call that function in order to derive the base_fee_per_gas from the parent block parameters.
2. Currently, the fork block in Arrow Glacier and Gray Glacier forks has INITIAL_BASE_FEE as the base fee. This was originally meant to be true only in case of London.

Related to Issue #625

How was it fixed?

This commit performs refactors and simplifies the base fee calculation and also corrects the bug in Arrow Glacier and Gray Glacier.

Cute Animal Picture

[codecov-commenter]

Codecov Report

Patch coverage: 89.47% and project coverage change: +2.63 :tada:

Comparison is base (cebd3bc) 82.48% compared to head (8ca6d26) 85.11%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #743 +/- ## ========================================== + Coverage 82.48% 85.11% +2.63% ========================================== Files 570 570 Lines 31571 31557 -14 ========================================== + Hits 26040 26860 +820 + Misses 5531 4697 -834 ``` | Flag | Coverage Δ | | |---|---|---| | unittests | `85.11% <89.47%> (+2.63%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ethereum#carryforward-flags-in-the-pull-request-comment) to find out more. | [Impacted Files](https://codecov.io/gh/ethereum/execution-specs/pull/743?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ethereum) | Coverage Δ | | |---|---|---| | [src/ethereum/arrow\_glacier/fork.py](https://codecov.io/gh/ethereum/execution-specs/pull/743?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ethereum#diff-c3JjL2V0aGVyZXVtL2Fycm93X2dsYWNpZXIvZm9yay5weQ==) | `57.19% <75.00%> (+6.82%)` | :arrow_up: | | [src/ethereum/gray\_glacier/fork.py](https://codecov.io/gh/ethereum/execution-specs/pull/743?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ethereum#diff-c3JjL2V0aGVyZXVtL2dyYXlfZ2xhY2llci9mb3JrLnB5) | `57.19% <75.00%> (+6.82%)` | :arrow_up: | | [src/ethereum/london/fork.py](https://codecov.io/gh/ethereum/execution-specs/pull/743?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ethereum#diff-c3JjL2V0aGVyZXVtL2xvbmRvbi9mb3JrLnB5) | `93.28% <100.00%> (+1.06%)` | :arrow_up: | | [src/ethereum/paris/fork.py](https://codecov.io/gh/ethereum/execution-specs/pull/743?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ethereum#diff-c3JjL2V0aGVyZXVtL3BhcmlzL2ZvcmsucHk=) | `94.23% <100.00%> (ø)` | | | [src/ethereum/shanghai/fork.py](https://codecov.io/gh/ethereum/execution-specs/pull/743?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ethereum#diff-c3JjL2V0aGVyZXVtL3NoYW5naGFpL2ZvcmsucHk=) | `83.40% <100.00%> (ø)` | | ... and [40 files with indirect coverage changes](https://codecov.io/gh/ethereum/execution-specs/pull/743/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ethereum) Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ethereum). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ethereum)

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[gurukamath]

Added the feature to derive base_fee_per_gas from parent in t8n