conandeps: add progress output, silence Conan's SyntaxWarnings, allow Python 3.12+

- Progress lines on stderr for each of the three graph resolutions (with
  package/missing counts and timing) so a slow remote no longer looks like
  a hang; -q suppresses them. stdout remains the clean report.
- --verbose now streams Conan's output live via a tee instead of dumping it
  at the end.
- Filter SyntaxWarning/DeprecationWarning before importing conans: Conan 1.x
  modules trip the stricter escape-sequence checks of recent Pythons and
  printed a screenful of noise on 3.14.
- Drop the <3.12 requires-python ceiling. Conan 1.66 falls back to importlib
  where imp is missing; verified working on 3.14. Fix the Containerfile and
  docs that claimed otherwise.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EYNdaGDrpaqDyT8QtrTQbM

Containerfile

@@ -1,6 +1,6 @@
 # Development / runtime container for the conan utilities.
-# Pinned to Conan 1.66 (the version we target) on Python 3.11 — Conan 1.x
-# still imports the `imp` module, which was removed in Python 3.12.
+# Pinned to Conan 1.66 (the version we target). Python 3.11 is the newest
+# version Conan 1.x was released against; it also runs on newer Pythons.
 FROM docker.io/library/python:3.11-slim-bookworm
 
 ARG BUILD_DATE