feat(posfilter): Create loaders for wave glider L1 data for roll-pitch-heading and their std-devs

[madhavmk]

• New loader "read_raw_l1_data_files()" for reading L1 data file efficiently using regex pattern matching INSPVAA / INSSTDDEVA data formats.
• gps_ws_time_to_j2000_time() function to convert GPS weeks and seconds to seconds from J2000 epoch
• Add unittests to improve coverage
• Closes Issue #226

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 53.12500% with 15 lines in your changes are missing coverage. Please review.

:exclamation: No coverage uploaded for pull request base (dev@ff1c78b). Click here to learn what that means.

Files	Patch %	Lines
src/gnatss/loaders.py	31.81%	15 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev #231 +/- ## ====================================== Coverage ? 49.80% ====================================== Files ? 17 Lines ? 1036 Branches ? 0 ====================================== Hits ? 516 Misses ? 520 Partials ? 0 ```

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[madhavmk]

Hello @lsetiawan , Thank you for the valuable PR comments. I have addressed them.