Enable `fast` feature of ed25519-dalek #199

Job	Run time
Bench (current, refs/pull/190/merge)	4m 1s
Test Suite (stable)	4m 12s
Bench (base, main)	3m 52s
Rustfmt	29s
Test Suite (beta)	4m 21s
Builds (ubuntu-22.04, aarch64-linux-android)	1m 36s
Test Suite (1.70.0)	5m 1s
Builds (ubuntu-22.04, x86_64-unknown-linux-musl)	1m 33s
Builds (ubuntu-22.04, wasm32-unknown-unknown, --features wasm --no-default-features)	1m 15s
Builds (macos-13, aarch64-apple-ios)	2m 25s
Builds (macos-13, x86_64-apple-darwin)	2m 29s
Builds (macos-14, aarch64-apple-darwin)	1m 13s
Builds (windows-2019, x86_64-pc-windows-msvc)	4m 49s
Upload benchmark results	53s
	38m 9s

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