refactor(util): modern type hints + drop vestigial py2 __future__ imports

[randomizedcoder]

Modernize the util/ Python: type hints + drop vestigial py2 __future__

These util/ scripts already run under Python 3 (every one has a python3 shebang), but they still carried Python-2-straddle idioms and had no type annotations. This is a dedicated, review-focused modernization pass — separate from the W605 regex fix in #9 so each PR stays about one thing.

What changed

• Removed from __future__ import division, print_function (14 files). Both features are the default in Python 3, so these lines were no-ops. ruff flags them as UP010.
• Added PEP 585 / PEP 604 type annotations to every function: built-in generics (list[...], dict[...], tuple[...]) and X | None unions — never typing.List / Optional. typing.Any is used where a function returns a matplotlib Axes or a dict_keys view. Each file that gains annotations gets a single from __future__ import annotations, so the hints are lazy strings with zero runtime cost (and work on older 3.x too).
• avg.py: corrected a stale #!/usr/bin/env python shebang to python3, matching the rest of util/.

Bonus: three real Python-2 bugs fixed in diff_metrics.py

While annotating I found genuine py2 leftovers that raise NameError under python3 on their code paths (they sit on the "metric changed" / usage-error paths, which is why they'd survived):

-        metrics[match.group(1)] = long(match.group(2))
+        metrics[match.group(1)] = int(match.group(2))
...
-        value = long(match.group(2))
+        value = int(match.group(2))
...
-    printf("Usage: %s file file2\n" % sys.argv[0])
+    print("Usage: %s file file2\n" % sys.argv[0])

diff_metrics.py now runs end-to-end (verified the changed-metric path, including its %lu format — which is valid in python3, the l length modifier is accepted and ignored).

Scope

• The two large scripts — tthoma.py (14,774 lines) and cperf.py (1,984) — are intentionally left for follow-up PRs to keep this one reviewable.
• strip_decl.py already had neither a __future__ line nor functions, so it is unchanged.
• Broader idiom cleanup (f-strings over %, pathlib, removing unused imports) is deliberately out of scope here.

Verification

• All 18 changed files byte-compile (python -m py_compile).
• ruff --select UP010 over these files: 14 → 0.
• No legacy typing constructs introduced: ruff --select UP006,UP007,UP035,UP045 clean.
• Annotation names resolve: ruff --select F821 clean (the only F821 hits were the long/printf py2 bugs above, now fixed).
• Several scripts smoke-tested via stdin (avg, ttrange, ttoffset, ttgrep, diff_metrics).

Type annotations are lazy here — a safety note

Because every annotated file carries from __future__ import annotations (PEP 563), the annotations are never evaluated at runtime, so they cannot change behavior; they exist for readers, editors, and type checkers. Nothing in these scripts introspects annotations at runtime.