Support external blob

[BraveY]

Relevant Issue (if applicable)

If there are Issues related to this PullRequest, please list it.

Details

Please describe the details of PullRequest.

Types of changes

What types of changes does your PullRequest introduce? Put an x in all the boxes that apply:

• Bug fix (non-breaking change which fixes an issue)
• [x ] New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation Update (if none of the other choices apply)

Checklist

Go over all the following points, and put an x in all the boxes that apply.

• I have updated the documentation accordingly.
• I have added tests to cover my changes.

[codecov]

Codecov Report

Attention: Patch coverage is 56.87402% with 825 lines in your changes missing coverage. Please review.

Project coverage is 55.16%. Comparing base (7e51479) to head (9592ed1).

Files with missing lines	Patch %	Lines
contrib/nydusify/pkg/converter/converter.go	71.31%	76 Missing and 29 partials ⚠️
builder/src/directory.rs	0.00%	88 Missing ⚠️
builder/src/core/node.rs	23.76%	72 Missing and 5 partials ⚠️
contrib/nydusify/pkg/external/modctl/remote.go	58.77%	36 Missing and 18 partials ⚠️
contrib/nydusify/pkg/external/modctl/modctl.go	80.08%	36 Missing and 9 partials ⚠️
...trib/nydusify/pkg/snapshotter/external/external.go	53.60%	30 Missing and 15 partials ⚠️
storage/src/backend/external/meta.rs	0.00%	40 Missing ⚠️
builder/src/core/context.rs	51.28%	31 Missing and 7 partials ⚠️
src/bin/nydus-image/main.rs	0.00%	37 Missing ⚠️
storage/src/backend/external/mod.rs	10.00%	36 Missing ⚠️
... and 24 more

❗ There is a different number of reports uploaded between BASE (7e51479) and HEAD (9592ed1). Click for more details.

HEAD has 2 uploads less than BASE

Flag	BASE (7e51479)	HEAD (9592ed1)
	3	1

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1672      +/-   ##
==========================================
- Coverage   60.42%   55.16%   -5.26%     
==========================================
  Files         146      199      +53     
  Lines       48943    55359    +6416     
  Branches    46380    46978     +598     
==========================================
+ Hits        29573    30541     +968     
- Misses      17906    23242    +5336     
- Partials     1464     1576     +112     

Files with missing lines	Coverage Δ
api/src/config.rs	88.78% <100.00%> (+0.03%)	⬆️
builder/src/core/bootstrap.rs	77.63% <100.00%> (+0.29%)	⬆️
builder/src/core/chunk_dict.rs	70.18% <ø> (ø)
builder/src/core/tree.rs	80.86% <100.00%> (-0.02%)	⬇️
builder/src/merge.rs	70.73% <100.00%> (ø)
builder/src/stargz.rs	75.00% <100.00%> (+0.14%)	⬆️
builder/src/tarball.rs	63.26% <100.00%> (+0.57%)	⬆️
contrib/nydusify/pkg/cache/cache.go	39.90% <100.00%> (ø)
...trib/nydusify/pkg/chunkdict/generator/generator.go	0.00% <ø> (ø)
contrib/nydusify/pkg/committer/commiter.go	0.00% <ø> (ø)
... and 44 more

... and 37 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[BraveY]

@codecov retest