Post-review follow-ups for Graph send (#825/#826) and requests-to-httpx migration (#827)

Follow-ups from the review of PR #825 (whose implementation had already
landed on master via #826's stacked merge):

- Honor the documented [smtp] attachment and [smtp] message options.
  Both were parsed into opts but never passed to either summary-email
  transport (also broken in released 10.2.2), so a configured custom
  attachment filename or message body was silently ignored. Both the
  SMTP and Microsoft Graph transports now receive them, and the missing
  smtp_attachment Namespace default is added (also covers SIGHUP
  reload, which rebuilds opts from the CLI Namespace).
- Don't mislabel non-Graph mailbox errors as Microsoft Graph failures:
  the shared mailbox-fetch and watch handlers now log a generic
  "Mailbox Error" with traceback when the connection isn't Graph.
- Declare microsoft-kiota-abstractions as a direct dependency (imported
  directly in cli.py for Graph error handling; previously transitive).

Migrate all runtime HTTP from requests to httpx (webhook client, Splunk
HEC client, and the PSL-overrides / IP-database / reverse-DNS-map /
IPinfo-API fetches in utils.py):

- follow_redirects=True everywhere to preserve requests' default
  redirect-following; httpx does not follow redirects by default.
- The PSL-overrides and reverse-DNS-map fetches gain a 60s timeout
  (previously none), matching the IP-database fetch.
- response.ok -> response.is_success; requests.RequestException ->
  httpx.HTTPError; raw string bodies use content= (httpx's data= is
  form-encoding only); Splunk HEC verification moves to client
  construction (httpx has no per-request verify).
- requests drops out of [project] dependencies and moves to the [build]
  extra for the out-of-wheel maintainer script collect_domain_info.py,
  which deliberately stays on requests/urllib3 for its permissive-TLS
  adapter.
- Remove the requests-era module-level
  urllib3.disable_warnings(InsecureRequestWarning) in splunk.py; httpx
  doesn't route through urllib3, so its only remaining effect was
  globally silencing insecure-TLS warnings from other urllib3-based
  components as an import side effect. Nothing imports urllib3 directly
  anymore, so it also leaves [project] dependencies.

Tests: config-to-transport wiring for attachment/message on both
transports (including defaults), non-Graph errors keep the generic log
line, webhook/Splunk payload assertions moved to content=, and Splunk
verify asserted at httpx.Client construction. 736 passed; ruff and
pyright clean.

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

tests/test_webhook.py

@@ -49,7 +49,7 @@ class TestWebhookClientSaveMethods(unittest.TestCase):
         client.session = MagicMock()
         client.save_aggregate_report_to_webhook('{"agg": 1}')
         client.session.post.assert_called_once_with(
-            "http://agg.example.com", data='{"agg": 1}', timeout=60
+            "http://agg.example.com", content='{"agg": 1}', timeout=60
         )
 
     def test_failure_posts_to_failure_url(self):
@@ -57,7 +57,7 @@ class TestWebhookClientSaveMethods(unittest.TestCase):
         client.session = MagicMock()
         client.save_failure_report_to_webhook('{"fail": 1}')
         client.session.post.assert_called_once_with(
-            "http://fail.example.com", data='{"fail": 1}', timeout=60
+            "http://fail.example.com", content='{"fail": 1}', timeout=60
         )
 
     def test_smtp_tls_posts_to_smtp_tls_url(self):
@@ -65,7 +65,21 @@ class TestWebhookClientSaveMethods(unittest.TestCase):
         client.session = MagicMock()
         client.save_smtp_tls_report_to_webhook('{"tls": 1}')
         client.session.post.assert_called_once_with(
-            "http://tls.example.com", data='{"tls": 1}', timeout=60
+            "http://tls.example.com", content='{"tls": 1}', timeout=60
+        )
+
+
+class TestWebhookClientDictPayload(unittest.TestCase):
+    """``_send_to_webhook`` accepts ``bytes | str | dict``. httpx only
+    form-encodes a dict via ``data=``; string/bytes payloads must use
+    ``content=`` since httpx's ``data=`` is form-encoding only."""
+
+    def test_dict_payload_uses_data_kwarg(self):
+        client = _client()
+        client.session = MagicMock()
+        client._send_to_webhook("http://agg.example.com", {"agg": 1})
+        client.session.post.assert_called_once_with(
+            "http://agg.example.com", data={"agg": 1}, timeout=60
         )