Write tests for all commands and refactor code to make it more testable

[SonuBardai]

Addresses https://github.com/SonuBardai/lockbox/issues/47

Write tests for commands:

• [x] add_password

• [x] generate_password

• [x] show_password

• [x] remove_password

• [x] list_passwords

• [x] copy_to_clipboard https://github.com/SonuBardai/lockbox/issues/43

• [x] print in PasswordStore

[codecov-commenter]

Codecov Report

Merging #50 (1450de2) into main (5a5a131) will increase coverage by 23.42%. The diff coverage is 51.91%.

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@@             Coverage Diff             @@
##             main      #50       +/-   ##
===========================================
+ Coverage   43.89%   67.31%   +23.42%     
===========================================
  Files           8        8               
  Lines         843      970      +127     
===========================================
+ Hits          370      653      +283     
+ Misses        473      317      -156     

Files Changed	Coverage Δ
src/cli/args.rs	89.89% <ø> (ø)
src/main.rs	0.00% <0.00%> (ø)
src/repl/mod.rs	0.00% <0.00%> (ø)
src/pass/mod.rs	77.00% <62.85%> (+49.09%)	:arrow_up:
src/cli/commands.rs	89.14% <86.48%> (+89.14%)	:arrow_up:
src/store/mod.rs	98.16% <96.87%> (+23.69%)	:arrow_up: