proxyd/fix: error rate tolerance

[felipe-op]

Description

This code fixes how we calculate the error rate.
tl;dr it adds a tolerance in which the error rate will be set to 0 until we have at least 10 data points.

When the sliding window has few data points, the error rate can be skewed quickly, causing the node to the banned. I.e. for an max error rate of 50%, it takes 1 error out of 2 requests to ban the node.

Also when the window is empty, it was previously causing an division by zero.

Tests

Manual

Invariants

n/a

Additional context

Original PR: #5542
This change is part of the Consensus Aware RPC Proxy: https://www.notion.so/oplabs/Consensus-Aware-RPC-Proxy-0138e029af814e4cbca2740c7888e02d

Metadata

• Fixes https://linear.app/optimism/issue/INF-195/fix-error-rate

TODOs

• Author or reviewer has added an entry to the current release notes draft, if appropriate. -- not applicable

[changeset-bot]

⚠️ No Changeset found

Latest commit: 283b80c

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR

[netlify]

✅ Deploy Preview for opstack-docs canceled.

Name	Link
🔨 Latest commit	283b80c
🔍 Latest deploy log	https://app.netlify.com/sites/opstack-docs/deploys/6453dd500ff7cd000728560a