🌐 [translation-sync] Improve clarity and fix typos in need_for_speed lecture

Syncs translation of lectures/need_for_speed.md with upstream source PR #523.

Changes include:
- Restructure 'Pure Python is slow' → 'Why is Pure Python Slow?' with new subsections
- Rewrite 'Why do we need them?' section (two reasons: Python is small, Python is slow)
- Add three acceleration strategies (vectorization, JIT, parallelization)
- Restructure parallelization section (multithreading before multiprocessing)
- Rewrite multiprocessing/multithreading definitions correctly
- Consolidate GPU/TPU sections into simpler structure
- Remove redundant subsections and blank lines
- Various wording improvements throughout

Source: QuantEcon/lecture-python-programming#523

Author: mmcky

.translate/state/need_for_speed.md.yml

@@ -1,5 +1,5 @@
-source-sha: 21f1ea0669031ccc0ee0194878439a87de5d248d
-synced-at: "2026-04-10"
+source-sha: c0a74f003dd77fc52558b7b402b0f058b6b31bf7
+synced-at: "2026-04-12"
 model: claude-sonnet-4-6
 mode: UPDATE
 section-count: 5