ed25519: use from_bytes instead of from in ed25519 serde::Deserializer

[ptrcnull]

Currently there's no way to catch the error when deserializing an invalid signature, because it uses Signature::from that panics:

signatures/ed25519/src/lib.rs

Lines 544 to 546 in e478469

	deserializer
	.deserialize_bytes(ByteArrayVisitor)
	.map(Signature::from)

[ptrcnull]

This seems to not have fixed the issue - as seen in the following stacktrace, try_into ends up calling the same Signature::from:

thread 'tokio-runtime-worker' panicked at 'invalid signature: signature::Error { source: None }', /home/demon/.cargo/registry/src/github.com-1ecc6299db9ec823/ed25519-1.5.1/src/lib.rs:332:38
stack backtrace:
   0: rust_begin_unwind
   1: core::panicking::panic_fmt
   2: core::result::unwrap_failed
   3: core::result::Result<T,E>::expect
             at /home/buildozer/aports/community/rust/src/rustc-1.60.0-src/library/core/src/result.rs:1022:23
   4: ed25519::Signature::new
             at /home/demon/.cargo/registry/src/github.com-1ecc6299db9ec823/ed25519-1.5.1/src/lib.rs:332:9
   5: <ed25519::Signature as core::convert::From<[u8; _]>>::from
             at /home/demon/.cargo/registry/src/github.com-1ecc6299db9ec823/ed25519-1.5.1/src/lib.rs:369:9
   6: <T as core::convert::Into<U>>::into
             at /home/buildozer/aports/community/rust/src/rustc-1.60.0-src/library/core/src/convert/mod.rs:546:9
   7: <T as core::convert::TryFrom<U>>::try_from
             at /home/buildozer/aports/community/rust/src/rustc-1.60.0-src/library/core/src/convert/mod.rs:601:12
   8: <T as core::convert::TryInto<U>>::try_into
             at /home/buildozer/aports/community/rust/src/rustc-1.60.0-src/library/core/src/convert/mod.rs:586:9
   9: <ed25519::Signature as serde::de::Deserialize>::deserialize::{{closure}}
             at /home/demon/.cargo/registry/src/github.com-1ecc6299db9ec823/ed25519-1.5.1/src/lib.rs:503:31
  10: core::result::Result<T,E>::and_then
             at /home/buildozer/aports/community/rust/src/rustc-1.60.0-src/library/core/src/result.rs:1311:22
  11: <ed25519::Signature as serde::de::Deserialize>::deserialize
             at /home/demon/.cargo/registry/src/github.com-1ecc6299db9ec823/ed25519-1.5.1/src/lib.rs:501:9

[aumetra]

TryFrom has a default implementation for every type that implements From (see here).
The change might use .try_into() now but it internally still calls the regular From implementation.

Rewriting the code like so should work:

(&bytes[..]).try_into().map_err(de::Error::custom)

[tarcieri]

Alas, these deserializers could use tests 😦

I think I like your original suggestion of using from_bytes