Enable `fast` feature of ed25519-dalek #197

Job	Run time
Rustfmt	2m 41s
Test Suite (stable)	6m 31s
Bench (current, refs/pull/190/merge)	6m 2s
Test Suite (beta)	6m 30s
Builds (ubuntu-22.04, aarch64-linux-android)	1m 39s
Bench (base, main)	6m 7s
Builds (ubuntu-22.04, x86_64-unknown-linux-musl)	1m 36s
Test Suite (1.70.0)	7m 10s
Builds (ubuntu-22.04, wasm32-unknown-unknown, --features wasm --no-default-features)	3m 30s
Builds (macos-13, aarch64-apple-ios)	4m 31s
Builds (macos-13, x86_64-apple-darwin)	2m 57s
Builds (macos-14, aarch64-apple-darwin)	3m 26s
Builds (windows-2019, x86_64-pc-windows-msvc)	6m 41s
Upload benchmark results	3m 10s
	1h 2m 31s

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