feat: expose MountFUSE / UnmountFUSE API

[dtrudg]

Move Mount and Unmount to pkg from internal.

Rename to xxxxFUSE to make it clear these are FUSE mounts, rather than anything else.

Fixes #206

[codecov-commenter]

Codecov Report

Merging #209 (7c54475) into master (3e8948f) will not change coverage.
The diff coverage is 0.00%.

❗ Current head 7c54475 differs from pull request most recent head 1ab2364. Consider uploading reports for the commit 1ab2364 to get more accurate results

@@           Coverage Diff           @@
##           master     #209   +/-   ##
=======================================
  Coverage   73.28%   73.28%           
=======================================
  Files          34       34           
  Lines        2650     2650           
=======================================
  Hits         1942     1942           
  Misses        567      567           
  Partials      141      141           

Impacted Files	Coverage Δ
internal/app/siftool/mount.go	0.00% <0.00%> (ø)
internal/app/siftool/unmount.go	0.00% <0.00%> (ø)
pkg/sif/mount.go	0.00% <0.00%> (ø)
pkg/sif/unmount.go	0.00% <0.00%> (ø)

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