DE-9847 Fallback to RFC3339 in RFC2822Time parser (#507)

DE-1723 Fix payload format for CreateAPIKey (#500)

DE-1542 Add check to CalcAlertsHMAC (#498)

DE-1542 Add VerifyAlertsWebhookSignFromRequest, VerifyAlertsWebhookSi…

…gn and CalcAlertsHMAC functions to verify Alerts Webhook (#496)

Update ValidateEmail to use provider_lookup parameter (#493)

The `mailbox_verification` is a v3 parameter, v4 expects a different one

Automate CHANGELOG.md update (#489)

DE-1538 Add endpoint for Running Inbox Placement Test (#487)

https://documentation.mailgun.com/docs/inboxready/api-reference/optimize/inboxready/inbox-placement/post-v4-inbox-tests#/docs/inboxready/api-reference/optimize/inboxready/inbox-placement/get-v4-inbox-sharing-public--shareid-

Bump github.com/oapi-codegen/runtime from 1.4.0 to 1.4.1 (#482)

Bump github.com/oapi-codegen/runtime from 1.2.0 to 1.3.0 (#477)

Add missing event fields from Mailgun API (#471)

## Summary

Adds missing fields from the Mailgun Events API that are returned in
responses but not captured by the current structs.

In particular, `last-message` will contain the actual error when the
failure reason is "old", and `recipient-provider` enables analyzing
delivery rates by email provider.

**Note:** These fields are not yet in Mailgun's official API docs but
are present in API responses.

## Changes

- **DeliveryStatus**: `last-code`, `last-message`, `bounce-type`,
`first-delivery-attempt-seconds`
- **Storage**: `region`, `env`
- **Generic**: `log-level`
- **Accepted**: `recipient-provider`, `api-key-id`
- **Delivered/Failed**: `recipient-provider`, `primary-dkim`

All new fields are marked as optional (`omitempty`) since I could not be
certain they're always returned.

## Evidence

Example `failed` event:

```json
{
  "event": "failed",
  "log-level": "error",
  "recipient-provider": "Other",
  "primary-dkim": "pdk1._domainkey.email.example.com",
  "delivery-status": {
    "code": 602,
    "last-code": 616,
    "bounce-type": "soft",
    "last-message": "unable to connect to MX servers: ...",
    "attempt-no": 25
  },
  "storage": {
    "key": "...",
    "env": "production",
    "region": "europe-west1",
    "url": "..."
  }
}
```

## Checks

- [x] `go test ./...` passes
- [x] `go fmt` applied


## Update

Addressed review feedback:

- Removed `omitempty` from all new fields (only used for unmarshalling)
- Removed `recipient-provider` from `Accepted`

---------

Co-authored-by: Vilen Topchii <32271530+vtopc@users.noreply.github.com>