Fix mismatched_lifetime_syntaxes linter warnings

[lazy404]

This fixes the

warning: hiding a lifetime that's elided elsewhere is confusing
 --> src/parse.rs:9:35
  |
9 | pub(crate) fn parse_packet(input: &[u8]) -> Result<Packet> {
  |                                   ^^^^^            ------ the same lifetime is hidden here
  |                                   |
  |                                   the lifetime is elided here
  |
  = help: the same lifetime is referred to in inconsistent ways, making the signature confusing
  = note: `#[warn(mismatched_lifetime_syntaxes)]` on by default

linter warnings.