feat(frost-core): simplify trait bounds, don't use the allocator in some places #1452

Job	Run time
actionlint	8s
build with MSRV (1.66.1)	1m 54s
build with default features	29s
Clippy	46s
build with no_std (ristretto255)	19s
Check Rust doc	26s
Rustfmt	10s
build with no_std (ed25519)	20s
Check if automatically generated code is up to date	21s
build with no_std (p256)	38s
build with no_std (secp256k1)	23s
test on beta	2m 26s
build with no_std (secp256k1-tr)	20s
build with no_std (rerandomized)	15s
	8m 55s

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