Type classes + tests restructuring + bug fixes

[joom]

This PR introduces first-class support for Rocq type classes (though incomplete for complex ones w.r.t. indices), restructures the testing infrastructure, and fixes several code generation bugs.

• Type Classes: Type classes are now extracted to C++ concepts with requires clauses, and type class instances become template structs with static methods. (closes Compilation of Rocq type classes to C++ concepts and structs #2)

• Testing: The test infrastructure was modernized with dune-based test rules replacing shell scripts. Also added new tests for records and type classes.

Test results:

Running Crane Tests
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

basics/
  ack                       ✓ pass
  add_one                   ✓ pass
  binom                     ✓ pass
  colist                    ✗ fail
  eqordshow                 ✓ pass
  graph                     ✗ fail
  ind_param                 ✗ fail
  isort                     ✗ fail
  levenshtein               ✗ fail
  list                      ✓ pass
  map                       ✓ pass
  module                    ✓ pass
  msort                     ✗ fail
  multi_ind_functor         ✓ pass
  mutual_functor            ✓ pass
  mutual_mod                ✓ pass
  nat_bde                   ✓ pass
  nat                       ✓ pass
  nested_mod                ✗ fail
  nested_tree               ✗ fail
  psort                     ✗ fail
  pstring                   ✗ fail
  qsort                     ✗ fail
  rapply                    ✓ pass
  regexp                    ✗ fail
  rev                       ✗ fail
  rmatch                    ✓ pass
  tokenizer                 ✓ pass
  top_bde                   ✓ pass
  top                       ✓ pass
  tree                      ✓ pass
  vec                       ✗ fail
  zip                       ✗ fail

monadic/
  experiment                ✗ fail
  free_monad                ✗ fail
  hash_bde                  ✓ pass
  hash                      ✓ pass
  io                        ✓ pass
  par                       ✗ fail
  simple_io                 ✗ fail
  stm                       ✗ fail
  thread                    ✗ fail
  vector                    ✗ fail

━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
Results: 21 passed, 22 failed, 43 total