refactor: replace closure validation rules with an enum

[orizi]

Only two validation rules exist (range-check and signature), so the boxed-closure ValidationRule mechanism was overdesign. Replace it with an enum holding both rules; the signature rule keeps its shared signatures map directly instead of capturing it in a closure.

BREAKING: ValidationRule and Memory::add_validation_rule are now pub(crate).

Based on #2391.

🤖 Generated with Claude Code

Performance

Expected: none — this is a code-size/complexity refactor. The allocation win for range-check validation (the hot rule) already landed in #2391; the signature rule runs verify per instance, where a boxed-closure call is immeasurable.

Measured (best-of-7 vs parent #2391 branch, local; noise ±2.4%): all 12 benchmarks within noise (−3.0% to +4.7%, mixed signs, no consistent direction). As expected, no performance change.
Methodology: cairo_programs/benchmarks/*.cairo compiled with cairo-lang 0.14 --proof_mode, run via cairo-vm-cli <prog>.json --layout all_cairo --proof_mode, hyperfine best-of-7 per binary, local x86-64 Linux. Noise floor (identical-code control pair): ±2.4%.

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This change is 

[github-actions]

Benchmark Results for unmodified programs 🚀

Command	Mean [s]	Min [s]	Max [s]	Relative
base big_factorial	2.215 ± 0.024	2.178	2.255	1.00
head big_factorial	2.218 ± 0.020	2.193	2.261	1.00 ± 0.01

Command	Mean [s]	Min [s]	Max [s]	Relative
base big_fibonacci	2.097 ± 0.025	2.070	2.158	1.01 ± 0.01
head big_fibonacci	2.078 ± 0.010	2.062	2.092	1.00

Command	Mean [s]	Min [s]	Max [s]	Relative
base blake2s_integration_benchmark	6.400 ± 0.042	6.357	6.475	1.00
head blake2s_integration_benchmark	6.437 ± 0.104	6.364	6.712	1.01 ± 0.02

Command	Mean [s]	Min [s]	Max [s]	Relative
base compare_arrays_200000	2.176 ± 0.020	2.150	2.223	1.00
head compare_arrays_200000	2.194 ± 0.027	2.171	2.249	1.01 ± 0.02

Command	Mean [s]	Min [s]	Max [s]	Relative
base dict_integration_benchmark	1.479 ± 0.003	1.474	1.483	1.00
head dict_integration_benchmark	1.518 ± 0.021	1.488	1.556	1.03 ± 0.01

Command	Mean [s]	Min [s]	Max [s]	Relative
base field_arithmetic_get_square_benchmark	1.133 ± 0.010	1.118	1.152	1.00 ± 0.01
head field_arithmetic_get_square_benchmark	1.128 ± 0.010	1.115	1.143	1.00

Command	Mean [s]	Min [s]	Max [s]	Relative
base integration_builtins	6.514 ± 0.149	6.403	6.876	1.01 ± 0.02
head integration_builtins	6.435 ± 0.039	6.392	6.492	1.00

Command	Mean [s]	Min [s]	Max [s]	Relative
base keccak_integration_benchmark	6.679 ± 0.069	6.606	6.824	1.00
head keccak_integration_benchmark	6.680 ± 0.113	6.579	6.972	1.00 ± 0.02

Command	Mean [s]	Min [s]	Max [s]	Relative
base linear_search	2.228 ± 0.016	2.208	2.252	1.01 ± 0.01
head linear_search	2.214 ± 0.012	2.197	2.228	1.00

Command	Mean [s]	Min [s]	Max [s]	Relative
base math_cmp_and_pow_integration_benchmark	1.644 ± 0.012	1.626	1.667	1.00
head math_cmp_and_pow_integration_benchmark	1.663 ± 0.011	1.643	1.681	1.01 ± 0.01

Command	Mean [s]	Min [s]	Max [s]	Relative
base math_integration_benchmark	1.527 ± 0.006	1.521	1.536	1.00
head math_integration_benchmark	1.545 ± 0.007	1.531	1.553	1.01 ± 0.01

Command	Mean [s]	Min [s]	Max [s]	Relative
base memory_integration_benchmark	1.303 ± 0.010	1.286	1.316	1.00
head memory_integration_benchmark	1.308 ± 0.006	1.301	1.317	1.00 ± 0.01

Command	Mean [s]	Min [s]	Max [s]	Relative
base operations_with_data_structures_benchmarks	1.570 ± 0.018	1.550	1.604	1.00
head operations_with_data_structures_benchmarks	1.580 ± 0.008	1.565	1.589	1.01 ± 0.01

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
base pedersen	509.5 ± 3.4	506.3	518.5	1.00 ± 0.01
head pedersen	508.9 ± 1.8	506.1	511.2	1.00

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
base poseidon_integration_benchmark	655.6 ± 2.5	653.0	661.1	1.00
head poseidon_integration_benchmark	657.9 ± 1.5	655.9	660.8	1.00 ± 0.00

Command	Mean [s]	Min [s]	Max [s]	Relative
base secp_integration_benchmark	1.725 ± 0.007	1.718	1.740	1.00
head secp_integration_benchmark	1.733 ± 0.025	1.714	1.789	1.00 ± 0.01

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
base set_integration_benchmark	656.0 ± 1.6	653.6	658.2	1.00
head set_integration_benchmark	663.1 ± 4.9	655.7	669.8	1.01 ± 0.01

Command	Mean [s]	Min [s]	Max [s]	Relative
base uint256_integration_benchmark	3.961 ± 0.027	3.921	4.004	1.00
head uint256_integration_benchmark	3.965 ± 0.027	3.942	4.015	1.00 ± 0.01

[codecov]

Codecov Report

❌ Patch coverage is 83.33333% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 96.23%. Comparing base (c610d41) to head (ca05e6f).

Files with missing lines	Patch %	Lines
vm/src/vm/runners/builtin_runner/signature.rs	76.31%	9 Missing ⚠️

Additional details and impacted files

@@                           Coverage Diff                           @@
##           claude/vm-execution-performance-32hi0c    #2395   +/-   ##
=======================================================================
  Coverage                                   96.23%   96.23%           
=======================================================================
  Files                                         107      107           
  Lines                                       37985    37978    -7     
=======================================================================
- Hits                                        36555    36549    -6     
+ Misses                                       1430     1429    -1     

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