docs: Add Scrapling guide

[vdusek]

Adds a guide for the Scrapling adaptive web scraping library in Apify Actors, following the structure of the existing scraping-library guides.

• docs/03_guides/07_scrapling.mdx — the guide: introduction & features, choosing a fetcher (HTTP vs. browser-based), a runnable example Actor, Apify Proxy integration, and running browser fetchers (DynamicFetcher/StealthyFetcher) with the required scrapling install step in the Dockerfile.
• code/07_scrapling.py — runnable single-file example: a recursive title scraper using Scrapling's async HTTP AsyncFetcher through Apify Proxy. code/07_scrapling_browser.py shows the browser-based variant.
• Quick-start guides list updated.

Verified locally (apify run) and on the Apify platform (build + run SUCCEEDED, correct dataset output via Apify Proxy), including the browser path. Lint + type-check pass.

Closes: #836

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.94%. Comparing base (24a6edb) to head (404bdfb).
⚠️ Report is 3 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #938   +/-   ##
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  Coverage   86.94%   86.94%           
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  Files          48       48           
  Lines        2942     2942           
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  Hits         2558     2558           
  Misses        384      384           

Flag	Coverage Δ
e2e	37.76% <ø> (+0.20%)	⬆️
integration	59.10% <ø> (+0.20%)	⬆️
unit	75.69% <ø> (ø)

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