Trackers are Iterables instead of Generators

[gawebb-dstl]

The trackers have been turned into iterables instead of generators. This allows trackers to be copied/ manipulated while producing tracks if needed.

Instead of for time, tracks in tracker.tracks_gen():
you now write
for time, tracks in tracker:

There should be no other changes to how the trackers function

[gawebb-dstl]

@sdhiscocks I've added a generator method (with a deprecation warning) into the base tracker so that the tracker will function as normal. This is so people's code doesn't (hopefully) break straight away

[sdhiscocks]

If we are going to make a change, we should probably extend this to all other classes that use the BufferedGenerator: Reader, Feeder, Detector, Simulator and Writer.

I think migrating to making these classes iterators (and thinking iterator rather than iterable to be clear on distinction) is good idea. This is more standard approach than using BufferedGenerator, which was kinda working around the fact the class instances were not iterable in the first place.

On key element of iterators, is subsequent calls to __iter__ shouldn't reset or modify the calls to __next__. I don't think this should be an issue, but may need to see when code changes. Note that one of readers that I made a change to in this PR breaks that, but should be easy to resolve.

[codecov]

Codecov Report

Merging #415 (5358490) into main (071abc8) will decrease coverage by 0.02%.
The diff coverage is 99.09%.

@@            Coverage Diff             @@
##             main     #415      +/-   ##
==========================================
- Coverage   94.37%   94.34%   -0.03%     
==========================================
  Files         154      154              
  Lines        7443     7463      +20     
  Branches     1414     1409       -5     
==========================================
+ Hits         7024     7041      +17     
- Misses        315      317       +2     
- Partials      104      105       +1     

Flag	Coverage Δ
integration	67.96% <48.18%> (-0.03%)	⬇️
unittests	91.73% <99.09%> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
stonesoup/tracker/simple.py	99.09% <98.66%> (+0.13%)	⬆️
stonesoup/reader/yaml.py	95.23% <100.00%> (+0.41%)	⬆️
stonesoup/tracker/base.py	100.00% <100.00%> (ø)
stonesoup/tracker/pointprocess.py	93.54% <100.00%> (-4.82%)	⬇️

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