Update Rust crate secp256k1 to 0.31

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
secp256k1	workspace.dependencies	minor	0.29 → 0.31

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Release Notes

rust-bitcoin/rust-secp256k1 (secp256k1)

v0.31.1

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• Update deprecation notes with since instead of TBD.

v0.31.0

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• Update rand to 0.9 #​788
• Create keys from owned array values instead of from references #​781
• Add from_u8_masked RecoveryId constructor #​778
• Update upstream to 0cdc758a56360bf58a851fe91085a327ec97685a (secp256k1-sys 0.6) #​764
• Add Keypair::sign_schnorr_no_aux_rand #​762
• Replace Message with Into<Message> in ECDSA signing API #​755
• Deprecate ElligatorSwiftParty in favor of Party #​752

v0.30.0

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• Allow signing variable-length messages #​706
• Bump MSRV to 1.63 #​709
• Deprecate Message::from_digest_slice in favor of Message::from_digest #​712
• Truncate debug output of SecretKey; tighten bitcoin_hashes dependency version #​722
• Simplify and improve consistency of secret key types' debug output #​726
• Simplify and improve consistency of public key types' debug output #​745
• Feature-gate KeyPair::from_str on global-context or alloc #​728
• Add infallible constructors for schnorr::Signature from byteslices #​730
• Deprecate slice-parsing methods in favor of array-parsing ones #​737
• Make RecoveryId an enum rather than integer #​743

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[AArnott]

Attempted to rebase this update onto current main.

secp256k1 0.31 resolves, but compilation fails in zcash_transparent with extensive bip32 trait-bound errors (SecretKey: PrivateKey, PublicKey: bip32::PublicKey, etc.). The current bip32 pre-release pin does not implement traits for secp256k1 0.31.

Blocked on a compatible bip32/transparent stack upgrade. Not including this in the bulk dependency PR for now.