tendermint: use k256::ecdsa::VerifyingKey as Secp256k1 key

[tony-iqlusion]

See #873 for background.

This changes the type re-exported as tendermint::public_key::Secp256k1 from a k256::EncodedPoint to a k256::ecdsa::VerifyingKey.

The main distinction this provides is validating the public key (i.e. making sure it provides a valid solution to the secp256k1 curve equation), whereas EncodedPoint provides no validation of the public key.

If there were ever a Signature::Secp256k1 variant added, this would also make it easy to perform signature verification.

[tony-iqlusion]

Hmm, these build failures seem unrelated?

   Compiling flume v0.10.6
error[E0658]: or-patterns syntax is experimental
Error:   --> /home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/flume-0.10.6/src/lib.rs:90:14
   |
90 |         let (Self::Full(msg) | Self::Disconnected(msg)) = self;
   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: see issue #54883 <https://github.com/rust-lang/rust/issues/54883> for more information

error[E0658]: or-patterns syntax is experimental
Error:    --> /home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/flume-0.10.6/src/lib.rs:128:14
    |
128 |         let (Self::Timeout(msg) | Self::Disconnected(msg)) = self;
    |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: see issue #54883 <https://github.com/rust-lang/rust/issues/54883> for more information

[codecov-commenter]

Codecov Report

Merging #900 (26d4a17) into master (f0b307c) will increase coverage by 0.0%.
The diff coverage is 60.0%.

@@          Coverage Diff           @@
##           master    #900   +/-   ##
======================================
  Coverage    69.7%   69.8%           
======================================
  Files         200     200           
  Lines       16326   16326           
======================================
+ Hits        11391   11398    +7     
+ Misses       4935    4928    -7     

Impacted Files	Coverage Δ
tendermint/src/validator.rs	70.0% <0.0%> (ø)
tendermint/src/public_key.rs	67.5% <58.3%> (+7.5%)	⬆️
tendermint/src/account.rs	90.4% <100.0%> (ø)
rpc/src/endpoint/blockchain.rs	40.0% <0.0%> (-60.0%)	⬇️
rpc/src/endpoint/validators.rs	20.0% <0.0%> (-30.0%)	⬇️
tendermint/src/abci/tag.rs	74.0% <0.0%> (-11.2%)	⬇️
tendermint/src/config.rs	60.8% <0.0%> (-0.9%)	⬇️
testgen/src/vote.rs	83.7% <0.0%> (-0.9%)	⬇️
tendermint/tests/config.rs	97.2% <0.0%> (-0.7%)	⬇️
testgen/src/header.rs	78.1% <0.0%> (-0.7%)	⬇️
... and 5 more

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[tony-iqlusion]

Opened #901 to deal with the flume-related issue

[thanethomson]

@tarcieri is it worth perhaps adding a .changelog entry for this? Seems like an enhancement we'd want people to know about?

[tony-iqlusion]

@thanethomson added in 768019d

[thanethomson]

Thanks @tony-iqlusion! 🙏