Remove unconditional retry error logging

[alloutflo]

Summary

• remove the unconditional console.error side effect from retry backoff
• keep retry timing and final rejection behavior unchanged
• add a regression test proving that a transient failure is retried successfully without writing to the application's error log

Fixes #684.

Testing

• full Jasmine suite: 85 specs passed
• npm run lint
• npm run build

AI assistance disclosure

OpenAI Codex was used to analyze, implement, and test this change. The diff and checks listed above were verified in the contribution workspace.

[alloutflo]

@ksvirkou-hubspot Maintainer handoff: this PR is ready for review, mergeable, up to date with master, and has no review comments or open threads. The repository’s lint and test workflows are push-only, so GitHub does not create an upstream PR check here. The full local Jasmine suite passes (85 specs), including the regression proving a transient retry succeeds without writing to console.error; lint and build also pass. Could you review the narrowly scoped logging removal when convenient?