Use bounded Range headers when probing stream headers (fixes 403 from YouTube)

[ManfryHub]

YouTube now answers 403 Forbidden to any request on googlevideo stream URLs that carries no Range header or an open-ended one (bytes=N-). Measured with curl on the URLs yt-dlp returned, same LAN / public IP, any User-Agent:

• GET + Range: bytes=0-1023 → 206
• GET without Range → 403 · GET + Range: bytes=0- → 403 · HEAD → 403

The main streaming loop already fetches bounded 128 KiB chunks and is fine, but the header probes done before playback (WebM::initialize, M4a::initialize) and the cue/sidx lookups used for seeking issued plain GETs, so every track failed with could not get codec info 403 Forbidden / could not get properties 403 Forbidden before a single byte was played (see issue #90).

This bounds those four requests:

• 256 KiB for the WebM header (EBML + SeekHead + Info + Tracks are within the first few KiB; the parser stops at WEBM_DONE);
• 128 KiB for the M4a atoms, matching the parser's existing 128*1024 cap;
• 1 MiB from the cues offset for WebM::getStartOffset.

Tested on Daphile 25.05 / LMS 9.0.3 / yt-dlp 2026.07.04 and nightly 2026.08.18: tracks play, seeking works. No other behaviour changed.