chore: remove unused ecdsa and signature dependencies

The p256/p384/p521 crates re-export ecdsa types and
signature traits internally. Detected by cargo-machete.

Author: nrdxp

Cargo.toml

@@ -20,14 +20,12 @@ serde_json = "1"
 digest    = "0.10"
 rand      = "0.8"
 sha2      = "0.10"
-signature = "2"
 thiserror = "1"
 
-# ECDSA curves
-ecdsa = { version = "0.16", features = ["signing", "verifying"] }
-p256  = { version = "0.13", features = ["ecdsa", "serde"] }
-p384  = { version = "0.13", features = ["ecdsa", "serde"] }
-p521  = { version = "0.13", features = ["ecdsa", "serde"] }
+# ECDSA curves (re-export ecdsa/signature traits internally)
+p256 = { version = "0.13", features = ["ecdsa", "serde"] }
+p384 = { version = "0.13", features = ["ecdsa", "serde"] }
+p521 = { version = "0.13", features = ["ecdsa", "serde"] }
 
 # Ed25519
 ed25519-dalek = { version = "2", features = ["serde", "rand_core"] }