fix!: allow colon and back slash in unix file name

[qweeah]

Resolves #695

To provide a file name with colon(:) and media-type at the same time, we can use backslash(\) to escape the colon in the file name, taking oras push as an example:

oras push some.reg/repo:tag "my\:file:my.media.type" # will push a file named `my:file` with mediatype `my.media.type`

Backslash can be used to escape itself:

oras push some.reg/repo:tag "my\\file:my.media.type" # will push a file named `my\file` with mediatype `my.media.type`

The old workaround still works after this change:

oras push some.reg/repo:tag my:file:my.media.type: # will push a file named `my:file` with mediatype `my.media.type`

Signed-off-by: Billy Zha jinzha1@microsoft.com

[codecov-commenter]

Codecov Report

Merging #734 (d9bfe6c) into main (cdeca2f) will increase coverage by 1.20%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #734      +/-   ##
==========================================
+ Coverage   73.17%   74.37%   +1.20%     
==========================================
  Files          16       16              
  Lines         574      601      +27     
==========================================
+ Hits          420      447      +27     
  Misses        123      123              
  Partials       31       31              

Impacted Files	Coverage Δ
cmd/oras/internal/fileref/unix.go	100.00% <100.00%> (ø)

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[TerryHowe]

Merge conflict

[qweeah]

Close as it's easier to use the workaround