NPI-3446 Fix SP3 parse and write of data section flags, plus address CLK and POS nodata causing misalignment

[treefern]

• fixed incorrect width of unused columns between data flag values (2 instead of 1). This allows the second prediction flag to be read in.
• Consolidated definitions of columns for maintainability.
• Updated column/index definitions to clearly define a FLAGS index, and specify names of individual flag columns.
• Fixed SP3 output generator to access and output FLAGS data.
• Addressed misalignment bug caused by the combination of CLK nodata value width, and Pandas adding a space between columns. Also applied this fix to POS nodata value, as it appears the same issue would apply there.
• Added handling for missing flag values (conformance to empty strings to avoid outputting nans)
• Added placeholder TODOs for throwing exceptions if record types are encountered that we currently do not implement support for (EP, EV).

[ronaldmaj]

Running this branch in python 3.12 via ipython I received the following warnings:

In [2]: from gnssanalysis.gn_io.sp3 import read_sp3, write_sp3
/data/review-repos/gnssanalysis/gnssanalysis/gn_io/blq.py:12: SyntaxWarning: invalid escape sequence '\/'
  _RE_LLH = _re.compile(b"lon\/lat\:\s+([\d\.]+)+\s+([\d\.\-]+)\s+([\d\.\-]+)")
/data/review-repos/gnssanalysis/gnssanalysis/gn_io/trop.py:76: SyntaxWarning: invalid escape sequence '\s'
  sep='\s+',

Not sure if we need to resolve these here, but something to take note of

[ronaldmaj]

Thanks for putting this PR together. It hits a lot of the issues we've been seeing recently in the Ginan-Ops space.

I found some errors in doing reading / writing cycles with example SP3 files. I think when these are resolved, this should be good to go in

[ronaldmaj]

Tested with various SP3 files from different ACs (COD, GFZ, WHU, GA) and different types (ULT, RAP, FIN). Seems to work great now!
Thanks for putting through those changes yesterday.
I think this now good to go in 👍

[treefern]

Running this branch in python 3.12 via ipython I received the following warnings:

In [2]: from gnssanalysis.gn_io.sp3 import read_sp3, write_sp3
/data/review-repos/gnssanalysis/gnssanalysis/gn_io/blq.py:12: SyntaxWarning: invalid escape sequence '\/'
  _RE_LLH = _re.compile(b"lon\/lat\:\s+([\d\.]+)+\s+([\d\.\-]+)\s+([\d\.\-]+)")
/data/review-repos/gnssanalysis/gnssanalysis/gn_io/trop.py:76: SyntaxWarning: invalid escape sequence '\s'
  sep='\s+',

Not sure if we need to resolve these here, but something to take note of

Resolved with use of raw string flag (i.e. 'rb"blah"). Testing on another example, it seems it should work either way, but this makes the linter happy.

[ronaldmaj]

Additional commits to address comment I made around the regex expression and leaving notes - minor changes that don't change the overall SP3 changes so happy for this to go in