hdl._dsl: raise an error when modifying an already-elaborated `Module`.

[wanda-phi]

Fixes #1350.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 91.04%. Comparing base (dde8334) to head (0d2f035). Report is 13 commits behind head on main.

:exclamation: Current head 0d2f035 differs from pull request most recent head 58223c2. Consider uploading reports for the commit 58223c2 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1352      +/-   ##
==========================================
+ Coverage   90.48%   91.04%   +0.56%     
==========================================
  Files          43       44       +1     
  Lines       10864    11126     +262     
  Branches     2660     2416     -244     
==========================================
+ Hits         9830    10130     +300     
+ Misses        855      817      -38     
  Partials      179      179              

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