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>

pyproject.toml

@@ -44,16 +44,21 @@ dependencies = [
     "dnspython>=2.0.0",
     "elasticsearch>=8.18,<9",
     "expiringdict>=1.1.4",
+    # The runtime HTTP library (utils.py fetches, webhook and Splunk HEC
+    # clients, Graph error handling in cli.py). The floor matches
+    # microsoft-kiota-http's own requirement.
+    "httpx>=0.25",
     "kafka-python>=2.3.2",
     "lxml>=4.4.0",
     "mailsuite[gmail,msgraph]>=2.2.2",
     "maxminddb>=2.0.0",
+    # Imported directly in cli.py for Graph error handling; otherwise
+    # only a transitive dep of mailsuite[msgraph] -> msgraph-sdk.
+    "microsoft-kiota-abstractions>=1.8.0",
     "opensearch-py>=2.4.2,<=4.0.0",
     "publicsuffixlist>=0.10.0",
     "pygelf>=0.4.2",
-    "requests>=2.22.0",
     "tqdm>=4.31.1",
-    "urllib3>=1.25.7",
     "xmltodict>=0.12.0",
     "PyYAML>=6.0.3"
 ]
@@ -81,6 +86,11 @@ build = [
     "pyright==1.1.410",
     "pytest",
     "pytest-cov",
+    # Used only by the out-of-wheel maintainer script
+    # parsedmarc/resources/maps/collect_domain_info.py, which deliberately
+    # stays on requests because its permissive-TLS fallback is built on
+    # urllib3's HTTPAdapter machinery.
+    "requests>=2.22.0",
     "ruff",
     "sphinx",
     "sphinx_rtd_theme",