Masking Changes and DataFrame Read and Write Capabilities

[ctuguinay]

For lines masking: Clean up how bottom_interpolated is constructed. Past version had unused variables. For regions2d masking: Made use of numbers instead of names in regionmask regions initialization so to work directly with the dimension region instead of having to switch coordinate names with dimension regions.

Also, solved problem where echoregions version cannot be imported in the top level __init__.py file of the package.

[codecov[bot]]

Codecov Report

Attention: 7 lines in your changes are missing coverage. Please review.

Comparison is base (3534c97) 87.23% compared to head (a06060a) 87.54%. Report is 3 commits behind head on main.

Files	Patch %	Lines
echoregions/regions2d/regions2d_parser.py	85.71%	3 Missing :warning:
echoregions/lines/lines_parser.py	89.47%	2 Missing :warning:
echoregions/lines/lines.py	93.75%	1 Missing :warning:
echoregions/regions2d/regions2d.py	91.66%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #148 +/- ## ========================================== + Coverage 87.23% 87.54% +0.30% ========================================== Files 14 13 -1 Lines 525 578 +53 ========================================== + Hits 458 506 +48 - Misses 67 72 +5 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[ctuguinay]

@leewujung, Here are some slight changes made corresponding to errors that I noticed when running echoregion functions in hake labels.

[ctuguinay]

An offshoot when I was looking at the tests: seems like there is a missing assert condition in the last line of test_mask_empty_no_overlap?

Just added this assert.

[ctuguinay]

Recent Changes:

• Added read and write capabilities for Lines and Regions2d objects
  • Reading comes with the assumption that the CSV or Dataframe contains depth and time columns (similar to Lines) when being read in as a Lines object or region_id, depth, and time columns (similar to Regions2d objects) when being read in as a Regions2d object.
• Added contour output for both Lines and Regions2d objects
  • Contour objects are dataframes that can be used to initialize new Lines or Regions2d objects respectively

[ctuguinay]

@leewujung This is ready to be reviewed again.