feat: add tx.pendingAt

[yqrashawn]

PORTAL-3423

---

This change is 

[AngeliaQ]

Task linked: PORTAL-3423 优化加速取消交易

[codecov]

Codecov Report

Merging #1263 (ef7d11e) into dev (587e7c7) will decrease coverage by 0.00%.
The diff coverage is 0.00%.

❗ Current head ef7d11e differs from pull request most recent head cd00069. Consider uploading reports for the commit cd00069 to get more accurate results

@@            Coverage Diff             @@
##              dev    #1263      +/-   ##
==========================================
- Coverage   24.56%   24.55%   -0.01%     
==========================================
  Files         606      606              
  Lines       38497    38498       +1     
  Branches     1324     1324              
==========================================
  Hits         9455     9455              
- Misses      28834    28835       +1     
  Partials      208      208              

Flag	Coverage Δ
unittests	24.55% <0.00%> (-0.01%)	⬇️

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

Impacted Files	Coverage Δ
packages/background/src/db-schema.js	0.00% <0.00%> (ø)

Help us with your feedback. Take ten seconds to tell us how you rate us.