stateDB txlog store enhancement

[JayT106]

Description

after profiling BenchmarkEmitLogs in #436
found we can improve the emit log speed by changing the log store structure.

Therefore, we store each log separately prefixlogkey | txHash | log.Index, not stores by []logs

The change improves the log store by around 90x within the testcase.

In #436:

goos: darwin
goarch: amd64
pkg: github.com/tharsis/ethermint/x/evm/keeper
cpu: Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz
BenchmarkEmitLogs-12    	       5	1197719670 ns/op

In This PR:

goos: darwin
goarch: amd64
pkg: github.com/tharsis/ethermint/x/evm/keeper
cpu: Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz
BenchmarkEmitLogs-12    	     453	  13216579 ns/op

Updated PR:

pkg: github.com/tharsis/ethermint/x/evm/keeper
cpu: Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz
BenchmarkEmitLogs
BenchmarkEmitLogs-12         	      97	  12626105 ns/op

---

For contributor use:

• Targeted PR against correct branch (see CONTRIBUTING.md)
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• 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)
• Reviewers assigned
• Squashed all commits, uses message "Merge pull request #XYZ: [title]" (coding standards)

[codecov]

Codecov Report

Merging #461 (443dffc) into main (7b3ceec) will increase coverage by 0.03%.
The diff coverage is 57.69%.

@@            Coverage Diff             @@
##             main     #461      +/-   ##
==========================================
+ Coverage   49.18%   49.22%   +0.03%     
==========================================
  Files          57       57              
  Lines        5363     5408      +45     
==========================================
+ Hits         2638     2662      +24     
- Misses       2608     2629      +21     
  Partials      117      117              

Impacted Files	Coverage Δ
x/evm/keeper/keeper.go	66.35% <46.77%> (-4.34%)	⬇️
x/evm/keeper/grpc_query.go	71.21% <100.00%> (+0.80%)	⬆️
x/evm/keeper/statedb.go	84.61% <100.00%> (-0.16%)	⬇️

[fedekunze]

See comment. I would like to propose a cleaner implementation that doesn't add a new store key and relies on the store Iterator to retrieve the logs

[orijbot]

Visit https://dashboard.github.orijtech.com?back=0&pr=461&remote=true&repo=JayT106%2Fethermint to see benchmark details.

[fedekunze]

ACK. Thanks @JayT106! Can you add a Changelog entry under the improvements section 🙏

[JayT106]

ACK. Thanks @JayT106! Can you add a Changelog entry under the improvements section 🙏

Sure, will do. Thanks for the review.