Apply Adisankar's native review round to python_by_example (100 flags)

Applies all 100 inline review comments from the calibration review on #1
(2026-08-07 through 2026-08-15). Each 'Preferred:' rendering is applied
verbatim, with minimal typographic normalisation: code spans and
cross-reference links restored where the plain-text comments dropped them
(ϵ_values, ts_length, for, f'foo{var}', the {doc} NumPy link, the
subpackage bold), straight quotes and single spaces, and one suspected
slip normalised (flag on line 381: ആയ -> ആയി) — listed for the reviewer's
verification in the PR comment.

Retain-in-English flags (comments on lines 106, 471, 489, 570, 583, 639,
and the ex5 hint and solution sections) take the English text byte-exact
from the source lecture at lecture-python-programming@81d9734.

Part of the Phase 2 calibration round tracked in QuantEcon/action-translation#189.

Co-Authored-By: Adisankar Manoj Thanuja <45125206+adisankarmt@users.noreply.github.com>
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: 3 people