feat: fix "Rule should start at 2" bug in MemoryAdapter::load_policy()

[liulifox233]

Rule should start at 2.

[github-actions]

Benchmark for d01ccdc

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Test	PR Benchmark	Master Benchmark	%
b_benchmark_rbac_model_large	10.9±0.05ms	10.0±0.13ms	+9.00%
benchmark priority model	4.2±0.08µs	4.2±0.04µs	0.00%
benchmark_abac_model	2.4±0.04µs	2.5±0.05µs	-4.00%
benchmark_basic_model	3.7±0.04µs	3.9±0.04µs	-5.13%
benchmark_key_match	6.8±0.14µs	6.7±0.10µs	+1.49%
benchmark_raw	0.0±0.00ns	0.0±0.00ns	NaN%
benchmark_rbac_model	6.2±0.09µs	6.1±0.07µs	+1.64%
benchmark_rbac_model_medium	953.0±7.03µs	854.9±12.62µs	+11.48%
benchmark_rbac_model_with_domains	5.8±0.06µs	6.0±0.12µs	-3.33%
benchmark_rbac_with_deny	8.7±0.10µs	8.3±0.11µs	+4.82%
benchmark_rbac_with_resource_roles	4.4±0.07µs	4.4±0.06µs	0.00%
benchmark_role_manager_large	4.5±0.15ms	4.6±0.08ms	-2.17%
benchmark_role_manager_medium	305.7±4.32µs	305.6±5.30µs	+0.03%
benchmark_role_manager_small	98.2±1.32µs	89.5±1.45µs	+9.72%