feat(rln): get_leaf ffi and public api

[rymnc]

Exposes the get_leaf fn to the public and ffi api's

[github-actions]

Benchmark for 56a0661

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Test	Base	PR	%
FullMerkleTree::compute_root	0.1±0.00ns	0.1±0.00ns	0.00%
FullMerkleTree::delete	1232.1±1.56ns	1202.5±1.85ns	-2.40%
FullMerkleTree::get	2.9±0.05ns	2.9±0.06ns	0.00%
FullMerkleTree::override_range	3.0±0.00µs	3.1±0.00µs	+3.33%
FullMerkleTree::set	1211.7±2.20ns	1213.8±5.00ns	+0.17%
OptimalMerkleTree::compute_root	1382.7±4.65ns	1390.3±2.44ns	+0.55%
OptimalMerkleTree::delete	1379.2±1.76ns	1380.3±18.89ns	+0.08%
OptimalMerkleTree::get	27.8±0.15ns	28.3±0.09ns	+1.80%
OptimalMerkleTree::override_range	7.2±0.01µs	7.1±0.05µs	-1.39%
OptimalMerkleTree::set	1380.7±15.10ns	1383.5±2.02ns	+0.20%

[github-actions]

Benchmark for 56a0661

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Test	Base	PR	%
Pmtree::compute_root	11.2±0.01ns	2.4±0.02ns	-78.57%
Pmtree::get	469.9±0.35ns	471.4±7.40ns	+0.32%
Pmtree::override_range	176.2±6.01µs	180.1±32.91µs	+2.21%
Pmtree::set	73.5±1.54µs	72.1±0.11µs	-1.90%
Pmtree:delete	72.5±0.18µs	72.7±0.04µs	+0.28%

[github-actions]

Benchmark for c0577da

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Test	Base	PR	%
FullMerkleTree::compute_root	0.0±0.00ns	0.0±0.00ns	NaN%
FullMerkleTree::delete	1269.8±0.68ns	1272.4±1.06ns	+0.20%
FullMerkleTree::get	3.0±0.00ns	3.0±0.00ns	0.00%
FullMerkleTree::override_range	3.2±0.00µs	3.2±0.00µs	0.00%
FullMerkleTree::set	1285.8±0.51ns	1271.3±3.73ns	-1.13%
OptimalMerkleTree::compute_root	1418.7±0.93ns	1424.0±1.58ns	+0.37%
OptimalMerkleTree::delete	1430.5±1.48ns	1433.0±0.87ns	+0.17%
OptimalMerkleTree::get	26.5±0.08ns	26.5±0.08ns	0.00%
OptimalMerkleTree::override_range	7.2±0.01µs	7.3±0.04µs	+1.39%
OptimalMerkleTree::set	1424.7±15.22ns	1422.8±1.04ns	-0.13%

[github-actions]

Benchmark for c0577da

Click to view benchmark

Test	Base	PR	%
Pmtree::compute_root	2.7±0.13ns	2.7±0.13ns	0.00%
Pmtree::get	585.3±122.79ns	600.8±54.18ns	+2.65%
Pmtree::override_range	242.3±18.47µs	238.5±24.60µs	-1.57%
Pmtree::set	86.2±5.10µs	89.8±6.76µs	+4.18%
Pmtree:delete	85.5±6.02µs	87.3±4.99µs	+2.11%

[tyshko-rostyslav]

LGTM