refactor(jstzd): use poll in retry

[huancheng-trili]

Context

Following #645.

Description

Reuse poll in retry since they do very similar things. Also added some tests for these two functions.

Manually testing the PR

• Unit test: added new test cases

[codecov]

Codecov Report

Attention: Patch coverage is 90.80460% with 8 lines in your changes missing coverage. Please review.

Project coverage is 46.98%. Comparing base (db88c9e) to head (773c507).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/jstzd/src/task/utils.rs	90.80%	0 Missing and 8 partials ⚠️

Files with missing lines	Coverage Δ
crates/jstzd/src/task/utils.rs	91.57% <90.80%> (+5.86%)	⬆️

---

Continue to review full report in Codecov by Sentry.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update db88c9e...773c507. Read the comment docs.