GetFileDeals should return deals for each file range

[xinaxu]

First step to address filecoin-project/motion#228
This changes GetFileDealsHandler to return list of deals for each FileRange.

[codecov]

Codecov Report

Attention: 6 lines in your changes are missing coverage. Please review.

Comparison is base (978935b) 74.20% compared to head (1093cb7) 74.23%.

❗ Current head 1093cb7 differs from pull request most recent head bd92f63. Consider uploading reports for the commit bd92f63 to get more accurate results

Files	Patch %	Lines
handler/file/deals.go	72.72%	4 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #423      +/-   ##
==========================================
+ Coverage   74.20%   74.23%   +0.02%     
==========================================
  Files         150      150              
  Lines        9926     9936      +10     
==========================================
+ Hits         7366     7376      +10     
  Misses       1806     1806              
  Partials      754      754              

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[gammazero]

LGTM, but check test errors:

panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xc0000005 code=0x0 addr=0x18 pc=0x7ff73e0aa5c3]

goroutine 41639 [running]:
github.com/data-preservation-programs/singularity/storagesystem.(*readerWithRetry).Close(0x7ff73c5c8675?)
	D:/a/singularity/singularity/storagesystem/rclone.go:166 +0x43
github.com/data-preservation-programs/singularity/store.(*PieceReader).Close(0x0?)
	D:/a/singularity/singularity/store/piece_store.go:328 +0x5a
github.com/data-preservation-programs/singularity/handler.download.func1(0x7)
	D:/a/singularity/singularity/handler/download.go:131 +0x8a9
created by github.com/data-preservation-programs/singularity/handler.download
	D:/a/singularity/singularity/handler/download.go:88 +0x377
FAIL	github.com/data-preservation-programs/singularity/cmd	125.491s