dekaf: Add support for not_before and not_after

[jshearer]

Description:

Now that we have MaterializationSpec::Bindings, we can support not_before, not_after, and also partition selectors.

---

This change is 

[jshearer]

With a binding of:

{
"bindings": [
    {
      "resource": {
        "topic_name": "wikichanges"
      },
      "source": {
        "name": "demo/wikipedia/recentchange-sampled",
        "notBefore": "2025-04-05T03:12:00Z",
        "notAfter": "2025-04-05T03:20:00Z"
      },
      "fields": {
        "recommended": true
      }
    }
  ]
}

Confirmed I only get data between 03:12:00Z and 03:20:00Z

$ kcat -o beginning -b dekaf-dev.estuary-data.com:9092 \
-X security.protocol=SASL_SSL \
-X sasl.mechanism=PLAIN \
-X sasl.username='estuary/jshearer/dekaf-notbefore-testing/dekaf-generic' \
-X sasl.password="..." -s value=avro -r 'https://estuary%2Fjshearer%2Fdekaf-notbefore-testing%2Fdekaf-generic:[email protected]' -e -G testing wikichanges | jq -c '.flow_published_at'

"2025-04-05T03:12:12.531248004Z"
"2025-04-05T03:12:13.542011704Z"
"2025-04-05T03:12:26.105103804Z"
"2025-04-05T03:12:27.193294404Z"
[...]
"2025-04-05T03:19:10.573997804Z"
"2025-04-05T03:19:39.380137004Z"
"2025-04-05T03:19:45.978076204Z"
"2025-04-05T03:19:55.043608104Z"

[jgraettinger]

LGTM