bugfix: marshal checkpoint by json

[WangZzzhe]

What type of PR is this?

Bug fixes

What this PR does / why we need it:

use json.Marshal instead of allocationInfo.Marshal() when turns podResourcesChk to checkpointData.
allocationInfo.Marshal() may produce invalid UTF-8 characters when some float value is greater than 1000, which causes verifyChecksum error after the encoding and decoding of the checkpoint.
bad cases are showed in pkg/agent/orm/pod_resource_test.go

Special notes for your reviewer:

@csfldf It seems that this issue may also occur in QRM？

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (5f147ea) 54.89% compared to head (3199ec3) 54.85%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #466      +/-   ##
==========================================
- Coverage   54.89%   54.85%   -0.05%     
==========================================
  Files         503      503              
  Lines       54778    54778              
==========================================
- Hits        30070    30046      -24     
- Misses      21469    21489      +20     
- Partials     3239     3243       +4     

Flag	Coverage Δ
unittest	54.85% <100.00%> (-0.05%)	⬇️

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