fix: substraction between relocatables should be signed

[Oppen]

It is valid as per the reference implementation to substract two relocatables a - b where b.offset > a.offset. The current code returns an error due to negative result in that case.
The fix consists in not using the trait as implemented for Relocatable (where it represents a positive distance between pointers) but to promote the offsets to i128 and only substract them for MaybeRelocatable, as those are the language-level types.

Checklist

• Linked to Github Issue
• Unit tests added
• Integration tests added.
• This change requires new documentation.
  • Documentation has been added/updated.
  • CHANGELOG has been updated.

[MegaRedHand]

LGTM. We can address TODOs and FIXMEs in following PRs.

[github-actions]

Benchmark Results for unmodified programs 🚀

Command	Mean [s]	Min [s]	Max [s]	Relative
base blake2s_integration_benchmark	15.357 ± 0.277	15.187	16.114	1.00
head blake2s_integration_benchmark	15.424 ± 0.346	15.131	16.353	1.00 ± 0.03

Command	Mean [s]	Min [s]	Max [s]	Relative
base compare_arrays_200000	4.980 ± 0.081	4.909	5.158	1.00 ± 0.02
head compare_arrays_200000	4.971 ± 0.077	4.905	5.172	1.00

Command	Mean [s]	Min [s]	Max [s]	Relative
base dict_integration_benchmark	3.258 ± 0.062	3.200	3.410	1.00
head dict_integration_benchmark	3.282 ± 0.027	3.255	3.343	1.01 ± 0.02

Command	Mean [s]	Min [s]	Max [s]	Relative
base factorial_multirun	5.287 ± 0.043	5.232	5.387	1.00
head factorial_multirun	5.340 ± 0.076	5.243	5.505	1.01 ± 0.02

Command	Mean [s]	Min [s]	Max [s]	Relative
base fibonacci_1000_multirun	4.533 ± 0.053	4.478	4.663	1.00
head fibonacci_1000_multirun	4.549 ± 0.024	4.502	4.582	1.00 ± 0.01

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
base field_arithmetic_get_square_benchmark	231.4 ± 21.3	214.4	270.2	1.07 ± 0.10
head field_arithmetic_get_square_benchmark	216.9 ± 1.9	213.3	219.8	1.00

Command	Mean [s]	Min [s]	Max [s]	Relative
base integration_builtins	14.191 ± 0.244	13.995	14.829	1.01 ± 0.02
head integration_builtins	14.097 ± 0.118	13.996	14.408	1.00

Command	Mean [s]	Min [s]	Max [s]	Relative
base keccak_integration_benchmark	15.596 ± 0.305	15.282	16.178	1.01 ± 0.02
head keccak_integration_benchmark	15.433 ± 0.073	15.290	15.534	1.00

Command	Mean [s]	Min [s]	Max [s]	Relative
base linear_search	4.954 ± 0.032	4.896	5.010	1.00
head linear_search	5.010 ± 0.069	4.894	5.115	1.01 ± 0.02

Command	Mean [s]	Min [s]	Max [s]	Relative
base math_cmp_and_pow_integration_benchmark	3.531 ± 0.030	3.484	3.590	1.00
head math_cmp_and_pow_integration_benchmark	3.552 ± 0.034	3.516	3.629	1.01 ± 0.01

Command	Mean [s]	Min [s]	Max [s]	Relative
base math_integration_benchmark	3.305 ± 0.049	3.261	3.421	1.00
head math_integration_benchmark	3.306 ± 0.037	3.266	3.397	1.00 ± 0.02

Command	Mean [s]	Min [s]	Max [s]	Relative
base memory_integration_benchmark	2.800 ± 0.016	2.778	2.825	1.00
head memory_integration_benchmark	2.812 ± 0.028	2.775	2.874	1.00 ± 0.01

Command	Mean [s]	Min [s]	Max [s]	Relative
base operations_with_data_structures_benchmarks	3.240 ± 0.019	3.218	3.286	1.00
head operations_with_data_structures_benchmarks	3.258 ± 0.019	3.228	3.288	1.01 ± 0.01

Command	Mean [s]	Min [s]	Max [s]	Relative
base pedersen	1.070 ± 0.010	1.051	1.082	1.00
head pedersen	1.076 ± 0.009	1.065	1.089	1.01 ± 0.01

Command	Mean [s]	Min [s]	Max [s]	Relative
base poseidon_integration_benchmark	1.863 ± 0.018	1.835	1.889	1.01 ± 0.01
head poseidon_integration_benchmark	1.852 ± 0.011	1.841	1.870	1.00

Command	Mean [s]	Min [s]	Max [s]	Relative
base secp_integration_benchmark	4.037 ± 0.032	3.989	4.071	1.00
head secp_integration_benchmark	4.079 ± 0.039	4.035	4.148	1.01 ± 0.01

Command	Mean [s]	Min [s]	Max [s]	Relative
base set_integration_benchmark	1.873 ± 0.030	1.838	1.937	1.01 ± 0.02
head set_integration_benchmark	1.853 ± 0.011	1.838	1.872	1.00

Command	Mean [s]	Min [s]	Max [s]	Relative
base uint256_integration_benchmark	9.771 ± 0.052	9.698	9.857	1.00
head uint256_integration_benchmark	9.814 ± 0.063	9.755	9.962	1.00 ± 0.01

[codecov]

Codecov Report

Merging #1218 (644f7f3) into main (061b2c3) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #1218   +/-   ##
=======================================
  Coverage   97.59%   97.59%           
=======================================
  Files          89       89           
  Lines       36159    36161    +2     
=======================================
+ Hits        35289    35291    +2     
  Misses        870      870           

Impacted Files	Coverage Δ
src/types/relocatable.rs	99.40% <100.00%> (+<0.01%)	⬆️

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