make lh5 types and exceptions picklable

[ManuelHu]

For reboost, I heavily use multiprocessing to produce optical maps. While testing things, I became aware of muliple issues concerning the usage of lgdos in a muti-process context.

• probably uncontroversial: make the esxeptions picklable (i.e. to propagate errors over process boundaries)
• it is quite useful to be able to transfer small LGDO objects (in my case, lgdo.types.Histogram.Axes) between processes. So I made them all picklable....
  This is partly based on @iguinn's work on the multiprocessing-capable LH5Iterator, and is extended to also support histogram pickling.
• I also added tests for many LGDO types, to see if pickling works.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.77%. Comparing base (f5ed430) to head (ef99e39).
Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #129      +/-   ##
==========================================
+ Coverage   78.65%   78.77%   +0.12%     
==========================================
  Files          46       46              
  Lines        3406     3421      +15     
==========================================
+ Hits         2679     2695      +16     
+ Misses        727      726       -1     

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[gipert]

Seems uncontroversial to me, merging.