Use transaction with optimistic lock to eliminate race

[metachris]

📝 Summary

Eliminate a possible race between multiple getPayload requests (until the Redis-write completes) by using an optimistically locked transaction.

See also:

• https://redis.uptrace.dev/guide/go-redis-pipelines.html#transactions
• https://github.com/redis/go-redis/blob/6ecbcf6c90919350c42181ce34c1cbdfbd5d1463/race_test.go#L183
• https://en.wikipedia.org/wiki/Optimistic_concurrency_control

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✅ I have run these commands

• make lint
• make test-race
• go mod tidy
• I have seen and agree to CONTRIBUTING.md

[michaelneuder]

looks great!

[codecov-commenter]

Codecov Report

Merging #365 (5e4bc80) into main (7c4fa2b) will increase coverage by 0.32%.
The diff coverage is 25.00%.

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@@            Coverage Diff             @@
##             main     #365      +/-   ##
==========================================
+ Coverage   19.37%   19.69%   +0.32%     
==========================================
  Files          20       20              
  Lines        3939     3965      +26     
==========================================
+ Hits          763      781      +18     
- Misses       3084     3091       +7     
- Partials       92       93       +1     

Flag	Coverage Δ
unittests	19.69% <25.00%> (+0.32%)	⬆️

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

Impacted Files	Coverage Δ
services/api/service.go	15.62% <0.00%> (-0.06%)	⬇️
datastore/redis.go	61.96% <85.71%> (+1.63%)	⬆️

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[metachris]

has been running a few days on goerli and sepolia

rolled out to Flashbots mainnet relay