Extract go-trustless-utils; and more improvements discovered along the way

[rvagg]

Primary things now in https://github.com/ipld/go-trustless-utils are:

• "verifiedcar" package from here is now called "traversal" over there
• misc http utilities that are also useful in Frisbii and should be generally useful
• basic types, DagScope, ByteRange and a Request type has been extracted that's a subset of what's now called RetrievalRequest here; the difference being that Request represents a Trustless Gateway request, while RetrievalRequest has lots of lassie extras on it.

Other things done in here, much of which was discovered while doing the extraction:

• removes "car-scope" handling
• minor changes to selector building for entity-bytes non-entity dag-scope
• improved error messages
• refactored traversal out of bitswapretriever
• major refactor/cleanup-reorg in /ipfs/ daemon handler
• return "bytes" in "Accept-Ranges" header (not "none")
• check dups parameter in content-type of HTTP remotes and handle accordingly

Includes some of the work I did in #386 around the traversal stuff — including collecting the LastPath so it can be dealt with elsewhere. I'm not currently using it here but I am using it in Frisbii to log cases where the requested path couldn't be completed in the DAG; I'll do the same here soon too for the CLI and close #386 out.

[codecov-commenter]

Codecov Report

Merging #404 (cf96aa6) into main (768f669) will decrease coverage by 1.23%.
The diff coverage is 91.08%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #404      +/-   ##
==========================================
- Coverage   77.00%   75.77%   -1.23%     
==========================================
  Files          87       84       -3     
  Lines        6700     6228     -472     
==========================================
- Hits         5159     4719     -440     
+ Misses       1267     1258       -9     
+ Partials      274      251      -23     

Files Changed	Coverage Δ
pkg/types/types.go	74.60% <ø> (-5.06%)	⬇️
cmd/lassie/fetch.go	31.84% <20.00%> (ø)
pkg/retriever/parallelpeerretriever.go	92.00% <50.00%> (ø)
pkg/retriever/retriever.go	87.75% <62.50%> (ø)
pkg/server/http/ipfs.go	89.31% <93.57%> (+1.58%)	⬆️
pkg/internal/testutil/mockroundtripper.go	87.92% <94.73%> (+2.28%)	⬆️
pkg/internal/itest/testpeer/peerhttpserver.go	68.93% <100.00%> (ø)
pkg/internal/testutil/gen.go	64.12% <100.00%> (-26.72%)	⬇️
pkg/retriever/assignablecandidatefinder.go	100.00% <100.00%> (ø)
pkg/retriever/bitswapretriever.go	96.01% <100.00%> (+1.61%)	⬆️
... and 3 more

... and 5 files with indirect coverage changes

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[rvagg]

Updated to ipld/go-trustless-utils#6 (will need to update again on tag)