Enable `fast` feature of ed25519-dalek #198

Job	Run time
Test Suite (stable)	6m 32s
Bench (current, refs/pull/190/merge)	6m 9s
Test Suite (beta)	6m 39s
Rustfmt	2m 43s
Bench (base, main)	3m 48s
Builds (ubuntu-22.04, aarch64-linux-android)	1m 36s
Test Suite (1.70.0)	7m 17s
Builds (ubuntu-22.04, x86_64-unknown-linux-musl)	1m 37s
Builds (ubuntu-22.04, wasm32-unknown-unknown, --features wasm --no-default-features)	3m 31s
Builds (macos-13, aarch64-apple-ios)	2m 40s
Builds (macos-13, x86_64-apple-darwin)	4m 43s
Builds (macos-14, aarch64-apple-darwin)	3m 32s
Builds (windows-2019, x86_64-pc-windows-msvc)	5m 15s
Upload benchmark results	3m 5s
	59m 7s

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