consistent baseFee check logic

[yihuang]

Closes: #755

Description

if not london_hardfork {
    # reject DynamicFeeTx
    # no `baseFeePerGas` field in block response
    # baseFee = nil
} else {
    # allow DynamicFeeTx
    # add `baseFeePerGas` field in block response
    if feemarketParams.NoBaseFee or height < feemarketParams.EnableHeight {
        # baseFee = 0
    } else {
        # init baseFee to initBaseFee and adjust in later blocks
    }
}

---

For contributor use:

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• Code follows the module structure standards.
• Wrote unit and integration tests
• Updated relevant documentation (docs/) or specification (x/<module>/spec/)
• Added relevant godoc comments.
• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md
• Re-reviewed Files changed in the Github PR explorer

---

For admin use:

• Added appropriate labels to PR (ex. WIP, R4R, docs, etc)
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[codecov]

Codecov Report

Merging #855 (29a51f2) into main (8bc3cc4) will decrease coverage by 0.16%.
The diff coverage is 50.79%.

❗ Current head 29a51f2 differs from pull request most recent head fb235dd. Consider uploading reports for the commit fb235dd to get more accurate results

@@            Coverage Diff             @@
##             main     #855      +/-   ##
==========================================
- Coverage   56.79%   56.63%   -0.17%     
==========================================
  Files          72       72              
  Lines        6060     6060              
==========================================
- Hits         3442     3432      -10     
- Misses       2420     2429       +9     
- Partials      198      199       +1     

Impacted Files	Coverage Δ
app/test_helpers.go	0.00% <0.00%> (ø)
x/feemarket/keeper/keeper.go	90.90% <ø> (ø)
x/evm/keeper/grpc_query.go	64.85% <45.83%> (-1.25%)	⬇️
app/ante/eth.go	83.95% <48.00%> (-0.80%)	⬇️
x/evm/keeper/keeper.go	79.88% <75.00%> (-0.59%)	⬇️
x/evm/keeper/state_transition.go	75.74% <100.00%> (-1.60%)	⬇️
x/evm/types/params.go	100.00% <100.00%> (ø)
... and 1 more

[fedekunze]

suggested changes LGTM. I'd add more test cases for the new behavior and also add a changelog entry.

[fedekunze]

ACK, can you add a changelog entry?

[yihuang]

ACK, can you add a changelog entry?

done, also added unit test for EvmKeeper.BaseFee.