More helpful record_full_arg errors

[hyanwong]

There are a few cases (e.g. the DTWF) where full_arg recording is not possible. We should give slightly more informative error messages when this is attempted. This PR should make it easy to add extra error messages for different cases like this.

[codecov]

Codecov Report

Merging #2143 (80a792f) into main (4e479ef) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #2143   +/-   ##
=======================================
  Coverage   91.43%   91.43%           
=======================================
  Files          19       19           
  Lines       11133    11136    +3     
  Branches     2266     2268    +2     
=======================================
+ Hits        10179    10182    +3     
  Misses        521      521           
  Partials      433      433           

Flag	Coverage Δ
C	91.43% <100.00%> (+<0.01%)	⬆️
python	98.73% <100.00%> (+<0.01%)	⬆️

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Impacted Files	Coverage Δ
msprime/ancestry.py	99.11% <100.00%> (+<0.01%)	⬆️

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[jeromekelleher]

LGTM - although this may be changing in the near future

Is it worth adding this now @GertjanBisschop?

[GertjanBisschop]

This should change in the near future indeed (see #2132). If the next msprime release is 1.3.0, then there probably is not much of a point in merging this. If there is going to be an earlier release, then I am all for the (temporary) more meaningful error message.

[GertjanBisschop]

Can be closed @hyanwong . Implemented in #2176.