Add shim CLI and sequencer

[po09i]

Description

Adds the ability to shim using the sequencer through st_b0shim. More precisely, the PR adds:

• st_b0shim CLI
• st_b0shim argument to use the sequencer (st_b0shim static, st_b0shim realtime, st_b0shim gradient_realtime)
• st_b0shim argument to define slices (st_b0shim define_slices) (Removed)
• Ability to define the slices using the "--slices" and "--slice-factor" options
• Define coil names in the constraints when defining a Coil
• Displays the R2 score of the linear fit in debug mode for rt sequencer
• Ability to output shim coefficients in different file formats
  • For realtime, available file formats: slicewise-ch, chronological-ch, eva
  • This allows for custom coils and scanner coils.
• Function to convert from physical CS to Gradient CS

To test

Run the tests in test/cli/test_cli_b0shim

Related

Fixes #101
Related to #297

[gaspardcereza]

Tested it locally and it works just fine. I went through the code and didn't spot any mistake/typo. LGTM !