Arabic: complete missing translations, fix NewPipe→PipePipe references, and address review feedback

[AhmedRX20]

This supersedes my earlier PR completing the Arabic (ar) translation, which was incomplete after being inherited from NewPipe. Closed that one to rebuild cleanly on the current v5.2.4 base file with all review feedback addressed from the start.

Original scope

• Added translations for missing keys that exist in base strings.xml but were absent from values-ar/strings.xml (SponsorBlock, SABR, ExoPlayer settings, filters, proxy, etc.)
• Fixed renamed (_new suffix) entries that still referenced "NewPipe" instead of "PipePipe"

Review feedback addressed (Thank you so much @my-live-is-a-lie) for the detailed review, and for the fix commit I built on top of

• Removed 24 obsolete keys no longer present in the base file
• Removed av_num (technical identifier, not meant to be translated)
• Fixed replies, subscribers, views, videos, watching, listening, days, deleted_downloads_toast plurals — correcting noun vs. verb-form confusion and dropping redundant %s where the Arabic quantity form makes the count implicit (zero/one/two)
• Replaced the literal "تعليقات الرصاصة" (bullet comments) with "التعليقات العائمة" (floating comments) across all 12 related keys — clearer for end users
• Changed "تجاوز" → "تخطي" in SponsorBlock strings for more natural phrasing
• Several smaller wording improvements (definite articles, more natural phrasing) on clear, clear_download_history, detail_drag_description, detail_uploader_thumbnail_view_description, error_path_creation, failed_streams, caption_setting_description

Full re-sync against base strings.xml v5.2.4

• Added missing translations for copyright, title_staff_list
• Added the missing limit_data_usage_description_list string-array (9 items)
• Removed 1 additional leftover key no longer in the base file
• Fixed terminology consistency: "تحميلات" → "تنزيلات" for downloads/downloads_title to match the term used everywhere else

Verified

• Key count matches base file 1:1 (961 strings, 14 plurals, 1 array), except av_num (intentionally untranslated)
• All %s/%d/%1$d placeholders match the base file exactly
• All 14 plurals have complete zero/one/two/few/many/other forms
• Valid XML, no syntax errors
• Machine-assisted translation, manually reviewed for terminology consistency (brand/technical names kept untranslated: YouTube, BiliBili, SponsorBlock, ExoPlayer, WebView, Ko-fi, etc.)

Ready for review.