refactor(hugr-py): simplify hugr replacement

[ss2165]

this exists as a tension between global/compositional building. Inter-graph edges necessitate global, all-at-once building for some cases. These update functions are required when inserting graphs in to other ones Instead replaced with new_nested classmethods inspired by #1192 (comment)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.61%. Comparing base (1da33e6) to head (c59b5fa).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1194      +/-   ##
==========================================
+ Coverage   86.58%   86.61%   +0.03%     
==========================================
  Files          96       96              
  Lines       18046    18079      +33     
  Branches    16831    16831              
==========================================
+ Hits        15625    15660      +35     
+ Misses       1647     1645       -2     
  Partials      774      774              

Flag	Coverage Δ
python	89.10% <100.00%> (+0.46%)	⬆️

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[ss2165]

@cqc-alec asking for re-review as the new new_nested approach is much simpler but quite different

[cqc-alec]

LGTM