feat: piecestorage support recursive lookup file

[simlecode]

关联的Issues (Related Issues)

close #464

改动 (Proposed Changes)

附注 (Additional Info)

自查清单 (Checklist)

在你认为本 PR 满足被审阅的标准之前，需要确保 / Before you mark the PR ready for review, please make sure that:

• 符合Venus项目管理规范中关于PR的相关标准 / The PR follows the PR standards set out in the Venus project management guidelines
• 具有清晰明确的commit message / All commits have a clear commit message.
• 包含相关的的测试用例或者不需要新增测试用例 / This PR has tests for new functionality or change in behaviour or not need to add new tests.
• 包含相关的的指南以及文档或者不需要新增文档 / This PR has updated usage guidelines and documentation or not need
• 通过必要的检查项 / All checks are green

[codecov-commenter]

Codecov Report

Merging #501 (e70dfb0) into master (6a7d921) will increase coverage by 0.17%.
The diff coverage is 96.49%.

❗ Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #501      +/-   ##
==========================================
+ Coverage   25.31%   25.49%   +0.17%     
==========================================
  Files         178      178              
  Lines       21026    21063      +37     
==========================================
+ Hits         5322     5369      +47     
+ Misses      14792    14785       -7     
+ Partials      912      909       -3     

Flag	Coverage Δ
unittests	25.49% <96.49%> (+0.17%)	⬆️

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

Files	Coverage Δ
piecestorage/filestore.go	70.00% <96.49%> (+20.48%)	⬆️

[LinZexiao]

LGTM