Fixing the SystemDbReader's handling of Object's Index/SortedIndex entry look-up

[jakrawcz-rdx]

This is a fix for a problem I encountered during development of Browse API's "get object collection entry" (see https://github.com/radixdlt/babylon-node/pull/755/files#diff-0a2c5a225e361800cb28568a6b51d0c0bbe1c5b5aded21ca10c783ef6fc0f743R174).

The SystemDatabaseReader was handling ObjectCollectionKey::KeyValue case just fine (i.e. it expected KeyValueEntrySubstate<V> values). However, for ObjectCollectionKey::Index/SortedIndex cases, it wrongfully expected the V values (without IndexEntrySubstate<V>/SortedIndexEntrySubstate<V> wrappers).

I unfortunately had to add the "unit" test in the radix-engine-tests (it cannot live next to SystemDatabaseReader since the SubstateDatabase impl required to run it is not available there).
(In general, the SystemDatabaseReader seems to have been developed as a test util [not covered by its own tests, but tested indirectly by assertions in tests of higher-level features], and I was not trying to change it in this PR)

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Benchmark for 4b3dc78

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Test	Base	PR	%
costing::bench_prepare_wasm	65.8±0.34ms	65.1±0.32ms	-1.06%
costing::decode_sbor	13.2±0.02µs	13.0±0.02µs	-1.52%
costing::decode_sbor_bytes	37.0±0.02µs	35.6±0.02µs	-3.78%
costing::deserialize_wasm	1253.6±1.42µs	1255.6±2.74µs	+0.16%
costing::instantiate_flash_loan	3.8±0.12ms	3.9±0.30ms	+2.63%
costing::instantiate_radiswap	5.3±0.08ms	5.2±0.06ms	-1.89%
costing::spin_loop	23.1±0.01ms	23.3±0.01ms	+0.87%
costing::validate_sbor_payload	25.6±0.02µs	25.9±0.02µs	+1.17%
costing::validate_sbor_payload_bytes	358.1±0.65ns	343.8±0.19ns	-3.99%
costing::validate_secp256k1	80.4±0.06µs	80.5±0.08µs	+0.12%
costing::validate_wasm	35.6±0.06ms	35.7±0.04ms	+0.28%
decimal::add/0	7.2±0.00ns	7.2±0.00ns	0.00%
decimal::add/rust-native	9.2±0.05ns	9.1±0.07ns	-1.09%
decimal::add/wasmer	139.8±0.26ns	139.1±0.10ns	-0.50%
decimal::add/wasmer-call-native	599.7±0.29ns	585.0±0.23ns	-2.45%
decimal::add/wasmi	478.4±1.45ns	474.7±10.25ns	-0.77%
decimal::add/wasmi-call-native	6.1±0.02µs	5.8±0.02µs	-4.92%
decimal::div/0	165.5±0.10ns	166.5±0.12ns	+0.60%
decimal::from_string/0	145.1±0.08ns	145.7±0.08ns	+0.41%
decimal::mul/0	128.9±0.11ns	128.6±0.10ns	-0.23%
decimal::mul/rust-native	132.9±0.05ns	131.8±0.06ns	-0.83%
decimal::mul/wasmer	1711.6±1.64ns	1709.6±0.94ns	-0.12%
decimal::mul/wasmer-call-native	716.1±0.21ns	713.0±0.37ns	-0.43%
decimal::mul/wasmi	29.9±0.06µs	30.2±0.03µs	+1.00%
decimal::mul/wasmi-call-native	6.2±0.02µs	6.1±0.02µs	-1.61%
decimal::pow/0	624.1±0.23ns	620.7±0.29ns	-0.54%
decimal::pow/rust-native	605.7±0.29ns	607.5±0.23ns	+0.30%
decimal::pow/wasmer	7.5±0.00µs	7.5±0.01µs	0.00%
decimal::pow/wasmer-call-native	1129.0±0.99ns	1121.4±0.19ns	-0.67%
decimal::pow/wasmi	140.7±0.27µs	144.7±0.17µs	+2.84%
decimal::pow/wasmi-call-native	5.8±0.03µs	5.4±0.03µs	-6.90%
decimal::root/0	9.1±0.00µs	9.3±0.00µs	+2.20%
decimal::sub/0	7.2±0.01ns	7.2±0.00ns	0.00%
decimal::to_string/0	494.0±0.44ns	493.6±0.22ns	-0.08%
precise_decimal::add/0	8.0±0.00ns	8.0±0.00ns	0.00%
precise_decimal::add/rust-native	10.4±0.02ns	10.4±0.01ns	0.00%
precise_decimal::add/wasmer	146.8±0.10ns	145.6±0.05ns	-0.82%
precise_decimal::add/wasmer-call-native	608.9±0.25ns	606.1±0.12ns	-0.46%
precise_decimal::add/wasmi	577.2±1.22ns	559.3±0.14ns	-3.10%
precise_decimal::add/wasmi-call-native	6.5±0.02µs	6.2±0.03µs	-4.62%
precise_decimal::div/0	264.4±0.06ns	261.5±0.09ns	-1.10%
precise_decimal::from_string/0	201.7±0.07ns	202.4±0.11ns	+0.35%
precise_decimal::mul/0	283.9±0.18ns	286.0±0.15ns	+0.74%
precise_decimal::mul/rust-native	259.9±0.47ns	261.0±0.07ns	+0.42%
precise_decimal::mul/wasmer	4.0±0.00µs	4.0±0.00µs	0.00%
precise_decimal::mul/wasmer-call-native	900.8±0.43ns	899.4±0.32ns	-0.16%
precise_decimal::mul/wasmi	78.7±0.15µs	78.6±0.02µs	-0.13%
precise_decimal::mul/wasmi-call-native	6.8±0.02µs	6.5±0.03µs	-4.41%
precise_decimal::pow/0	1574.3±0.37ns	1596.1±0.31ns	+1.38%
precise_decimal::pow/rust-native	1265.8±0.16ns	1265.6±0.43ns	-0.02%
precise_decimal::pow/wasmer	18.9±0.01µs	18.9±0.02µs	0.00%
precise_decimal::pow/wasmer-call-native	2.1±0.00µs	2.1±0.00µs	0.00%
precise_decimal::pow/wasmi	379.5±0.29µs	380.1±0.42µs	+0.16%
precise_decimal::pow/wasmi-call-native	11.2±0.02µs	11.1±0.03µs	-0.89%
precise_decimal::root/0	59.9±0.02µs	60.5±0.01µs	+1.00%
precise_decimal::sub/0	8.3±0.00ns	8.3±0.00ns	0.00%
precise_decimal::to_string/0	747.0±0.26ns	748.4±0.26ns	+0.19%
schema::validate_payload	285.3±0.20µs	284.1±0.26µs	-0.42%
transaction::radiswap	5.4±0.04ms	5.4±0.05ms	0.00%
transaction::transfer	1752.1±3.71µs	1739.4±3.60µs	-0.72%
transaction_processing::prepare	2.5±0.00ms	2.5±0.00ms	0.00%
transaction_processing::prepare_and_decompile	6.4±0.01ms	6.4±0.03ms	0.00%
transaction_processing::prepare_and_decompile_and_recompile	24.1±0.11ms	23.9±0.09ms	-0.83%
transaction_validation::validate_manifest	44.1±0.05µs	44.1±0.05µs	0.00%
transaction_validation::verify_ecdsa	78.0±0.09µs	78.0±0.06µs	0.00%
transaction_validation::verify_ed25519	52.8±0.07µs	52.7±0.03µs	-0.19%