Add footer

- Add a footer to each mail resulting from a split into an encrypted and
  an unencrypted version. The footer contains the recipients of the mail
  which are excluded in the corresponding stream.
- Move the construction of the `HuskContext` to the `mail`
  milter-command, as `helo` is used by scrapers to detect mailservers.
- Use `CertD::trust_root()` to get the trust root - it creates one if no
  root can be found.
- Add `chrono` dependency.

Cargo.lock

@@ -1261,6 +1261,7 @@ dependencies = [
  "aho-corasick",
  "anyhow",
  "bytes",
+ "chrono",
  "clap",
  "clap_complete",
  "daemonix",
@@ -2610,8 +2611,7 @@ checksum = "8a7852d02fc848982e0c167ef163aaff9cd91dc640ba85e263cb1ce46fae51cd"
 [[package]]
 name = "sequoia-cert-store"
 version = "0.7.3"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c4e07e420427eb5e0dc3bb61172d181fa3c87afb2a77e8c629e920f54a291a6d"
+source = "git+https://gitlab.com/sequoia-pgp/sequoia-cert-store?branch=malte%2Fassert_base_dir#ef9928239012a78b16be82b70420973a06e309a4"
 dependencies = [
  "anyhow",
  "crossbeam",
@@ -2624,7 +2624,7 @@ dependencies = [
  "sequoia-net",
  "sequoia-openpgp",
  "smallvec",
- "thiserror 2.0.18",
+ "thiserror 1.0.69",
  "tokio",
  "url",
 ]