Remove legacy Belt CPPO generator

[cristianoc]

Belt is a legacy API expected to be removed rather than developed further. Converting its frozen data-structure specializations to functors, or replacing CPPO with another generator, would add migration risk and maintenance machinery without improving the runtime users consume.

The checked-in specialized .res and .resi files were regenerated before this change and verified to be current. Make those files the canonical sources, and remove the CPPO templates, regeneration script, package command, OPAM dependency, and obsolete formatter exclusions. Normal builds already consumed the checked-in files, so this does not change runtime code or output.

Rename unrelated dotted-filename test inputs so no source or configuration references to CPPO remain. The changelog entries intentionally retain the name to document the removal across the stacked changes.

Checks: make test; make checkformat; dune build @check; dune build --profile browser --build-dir ./_build_playground compiler/jsoo/jsoo_playground_main.bc.js; dune exec tests/ounit_tests/ounit_tests_main.exe
Signed-off-by: Cristiano Calcagno cristianoc@users.noreply.github.com

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commit: 3a3928a

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.83%. Comparing base (6a6ef66) to head (3a3928a).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #8543   +/-   ##
=======================================
  Coverage   74.83%   74.83%           
=======================================
  Files         477      477           
  Lines       63311    63313    +2     
=======================================
+ Hits        47380    47382    +2     
  Misses      15931    15931           

Files with missing lines	Coverage Δ
tests/ounit_tests/ounit_string_tests.ml	97.09% <100.00%> (+0.01%)	⬆️

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