Use ahash for IndexMap and IndexSet hasher #12935
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The ahash hasher offers better performace as a drop in replacement for the stdlib hash algorithm. This is a large reason we use the hashbrown crate for our HashMap type in Qiskit (along with rayon support). The indexmap crate doesn't use ahash by default however, so we typically switch to it anywhere we use IndexMap or IndexSet to match the lookup performance of hashbrown in places where we need to preserve insertion order. However, there were a couple of spots where we missed this in the rust code, this commit corrects these oversights.
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In the `target_transpiler/mod.rs` module we were using ahash::HashSet for a hash set implementation, but the rest of Qiskit has standardized on using hashbrown for the `HashSet` and `HashMap` types. Hashbrown uses ahash for it's hashing algorithm but it also provides other advantages. To ensure that hash sets are compatible across the library we should be using the same library for everything. To support this goal, this commit also adds a clippy rule that raises a warning if the std library hashmap or hashset is used, or the versions from ahash. This means with our current dependency set the only allowed hashset types are `hashbrown::HashMap`/`HashSet` and `indexmap::IndexMap`/`IndexSet` (for where we need to maintain insertion order). Ideally we'd have a rule that forces the use of ahash with `IndexMap` and `IndexSet` (see Qiskit#12935) but I don't think clippy exposes an option to enable something like that.
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In the `target_transpiler/mod.rs` module we were using ahash::HashSet for a hash set implementation, but the rest of Qiskit has standardized on using hashbrown for the `HashSet` and `HashMap` types. Hashbrown uses ahash for it's hashing algorithm but it also provides other advantages. To ensure that hash sets are compatible across the library we should be using the same library for everything. To support this goal, this commit also adds a clippy rule that raises a warning if the std library hashmap or hashset is used, or the versions from ahash. This means with our current dependency set the only allowed hashset types are `hashbrown::HashMap`/`HashSet` and `indexmap::IndexMap`/`IndexSet` (for where we need to maintain insertion order). Ideally we'd have a rule that forces the use of ahash with `IndexMap` and `IndexSet` (see #12935) but I don't think clippy exposes an option to enable something like that.
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Summary
The ahash hasher offers better performace as a drop in replacement for the stdlib hash algorithm. This is a large reason we use the hashbrown crate for our HashMap type in Qiskit (along with rayon support). The indexmap crate doesn't use ahash by default however, so we typically switch to it anywhere we use IndexMap or IndexSet to match the lookup performance of hashbrown in places where we need to preserve insertion order. However, there were a couple of spots where we missed this in the rust code, this commit corrects these oversights.
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