feat(plugins): Register the standard matching rules and generators as core plugin capabilities

Proposal 009: let a plugin delegate a standard Pact rule to the host it is
running under, instead of reimplementing it. The mechanism has been in the
plugin driver since 006; nothing registered anything behind it, so a plugin
naming a standard rule resolved the catalogue entry and then failed with
"No core field matcher registered for 'type'".

Catalogue entries:

- the matcher entries are re-keyed by the name the rule carries in a
  request (`MatchingRule::name()`, the same string the driver puts in
  `MatchFieldRequest.rule.type`) rather than the specification version
  prefixed to the name, which moves to a `spec-version` value on the entry;
- generator entries are added - there were none at all, so `find_field_
  generator("Uuid")` failed at the catalogue step and no `generator/*`
  capability was ever advertised;
- both lists are now exactly the rules and generators this crate
  implements, pinned by a test that compares them against the enum
  variants, with an exhaustive match so a new variant fails to compile
  until it has an entry.

Handlers:

- `CoreFieldRuleMatcher` answers for the 16 rules that act on a single
  value, and `CoreFieldValueGenerator` for the 12 generators that are a
  pure function of their configuration and the test context;
- the collection-wide rules (`min-type`, `values`, `array-contains`,
  `each-key`/`each-value`) and the `ArrayContains` generator are
  registered too, but answer with why they can not be applied one value at
  a time - they stay host-only per 006's non-goals, and a plugin naming one
  should be told that rather than that nothing is registered;
- a rule or generator name this crate does not provide is an error, not a
  call back out: an unrecognised name parses into the `Plugin` carrier
  variant, which would send the callback straight back to a plugin.

Two bugs this turned up:

- `MatchingRule::Equality` on `&Bytes` built its mismatch message with
  `split_at(10)`, which panics for any value shorter than 10 bytes;
- rule and generator configuration crosses the plugin interface as a
  `google.protobuf.Struct`, which has one number type, so a plugin's
  `min: 2` arrives as `2.0` and the integer accessors reading it fall back
  to the attribute's default - a `RandomInt(5, 5)` from a plugin generated
  from `0..10`. Whole floats are put back to integers on the way in.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: rholshausen