Replaces local ChaCha20-Poly1305 with external crate

Migrates ChaCha20-Poly1305 encryption from the local crypto
module to rust-bitcoin's `chacha20-poly1305` crate.

Integrated the crate across all modules (Router,
PeerStorage, Onion Utils, etc.) and removed the deprecated internal
implementation. Updated test vectors to align with the new 12-byte
nonce construction and ensured SCID encryption remains consistent.

Author: Abeeujah

lightning/Cargo.toml

@@ -41,6 +41,7 @@ lightning-macros = { version = "0.2", path = "../lightning-macros" }
 bech32 = { version = "0.11.0", default-features = false }
 bitcoin = { version = "0.32.4", default-features = false, features = ["secp-recovery"] }
 
+chacha20-poly1305 = { git = "https://github.com/rust-bitcoin/rust-bitcoin.git", rev = "cdc27ae7c7426fc0a484e3b012a6cdbe6b10e85f", default-features = false }
 dnssec-prover = { version = "0.6", default-features = false }
 hashbrown = { version = "0.13", default-features = false }
 possiblyrandom = { version = "0.2", path = "../possiblyrandom", default-features = false }