Move `sameold::message::event` → `sameold::message::phenomenon`

Move SignificanceLevel and errors to
`sameold::message::significance`

These moves do not impact the external API.

* Drop enum variant `WeatherService`, which was previously emitted
  if sameold could not determine if the originator was the NWS or
  Environment Canda. It's actually easy to tell: in Canada, SAME
  is only ever transmitted on Weatherradio stations. This means
  the station callsign will be an `EC/…` station.

* Rename `Originator::as_str()` to `Originator::as_code_str()` for
  clarity

* Support the "alternate" format code.

* Originator is no longer `From<&str>`. Instead, it should be
  constructed via `Originator::from_org_and_call()`.

* Originator now implements Default

This is API-BREAKING for sameold. The samedec executable only
reports the Display value, which is largely unchanged, but a
`$SAMEDEC_ORIGINATOR` of "National Weather Service" will now be
emitted instead of "Weather Service."

* `SignificanceLevel::from()` constructs directly from
  significance code str. The conversion is infallible.
  A new `SignificanceLevel::Unknown` variant is returned
  when a significance level cannot be determined. It sorts
  higher than `Warning`.

* The conversion from `str` to `SignificanceLevel` is now
  infallible. A new `SignificanceLevel::Unknown` variant,
  which is the new Default, represents cases when the
  significance level cannot be determined.

* The UnknownSignificanceLevel is no longer required and
  is removed.

* Renamed `SignificanceLevel::as_str()` →
  `SignificanceLevel::as_code_str()`. This method returns a
  one-character significance code.

* The Unknown variant is the new Default.

This is an API-BREAKING change.

* The `EventCode` is now a struct which represents the combination
  of a `Phenomenon` and a `SignificanceLevel`.

  * The enum of all the SAME events is renamed to `Phenomenon`.

  * Phenomenon previously de-normalized into significance levels,
    like `TornadoWatch` and `TornadoWarning`, are represented as
    a single enum entry like `Tornado`.

  * Phenomenon from the 2022 revision of NWSI 10-1712 and more
    Canadian codes are added:

    * EAN: Renamed to National Emergency Message
    * NAT: National Audible Test
    * NST: National Silent Test
    * FSW: Flash Freeze Warning
    * FZW: Freeze Warning
    * HLS: Hurricane Local Statement
    * SQW: Snow Squall Warning

  * The alternate formatter for `EventCode` now displays only the
    phenomenon, like `Tornado`, without the significance level

* The conversion of `EventCode` from str is now infallible.
  Drop the `UnrecognizedEventCode` error.

* The `EventCodeIter` is not required and is dropped from the
  public API.

* Fix bad code entry for ADR (Administrative Message)

* Add dependency on `phf`

This is an API-BREAKING change.

The new API is simpler and doesn't require matches for errors.

The integration tests are also updated.