Modifications to the Pulsar class

[vhaasteren]

This PR does not add any new functionality or change any functionality. Instead, it slightly refactors the Pulsar class in a way that makes it easier to create derived classes without code replications.

Modifications:

• the classes PintPulsar and Tempo2Pulsar classes now have attributes drop_not_picklable, which initially was implemented in the base class.
• The par and tim files are also saved in strings as part of the pulsar object.
• Designmatrix units are saved
• The requested timing package in Pulsar is attempted to be used inside of a try block
• Add extra unit tests for full coverage

These modifications allow, for instance, for the h5pulsar package to be used as a drop-in replacement instead of the base Enterprise pulsar classes. The h5pulsar derives it's pulsar classes from Enterprise without code duplication. The modifications in this PR are completely independent from that package though, and simply make the code more modular.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.99%. Comparing base (daede07) to head (61ba269).

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #365      +/-   ##
==========================================
+ Coverage   86.74%   86.99%   +0.24%     
==========================================
  Files          13       13              
  Lines        3115     3144      +29     
==========================================
+ Hits         2702     2735      +33     
+ Misses        413      409       -4     

Files	Coverage Δ
enterprise/pulsar.py	93.54% <100.00%> (+1.44%)	⬆️

---

Continue to review full report in Codecov by Sentry.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update daede07...61ba269. Read the comment docs.

[AaronDJohnson]

@vhaasteren does storing the string data change the memory requirement for the object significantly?

[vhaasteren]

@vhaasteren does storing the string data change the memory requirement for the object significantly?

Significantly is a relative term. The tim files for some pulsars are several MB in size. Must be around 20MB for the largest pulsars in the IPTA? I didn't even think about it, but I suppose for an entire PTA it could add up.

Currently, it's stored if we set drop_t2pulsar=False or drop_pintpsr=False. Are you perhaps suggesting to make that a different option? My thinking was that, since saving the pulsar is optional, the usual analysis wouldn't be hindered in any way. The default is to drop the pulsar, meaning the par and tim files aren't saved either