Adding option to specify paths for input and output

[Sajjon]

Add CLI args to specify input paths for open and seal.

svar seal -i /path/to/secret.txt -o /path/to/sealed_secret.json

svar open -i /path/to/sealed_secret.json

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.98%. Comparing base (2e1066e) to head (e07a6bf).
⚠️ Report is 10 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main       #2   +/-   ##
=======================================
  Coverage   93.98%   93.98%           
=======================================
  Files          19       19           
  Lines         565      565           
=======================================
  Hits          531      531           
  Misses         34       34           

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