HLS live edge setting

[Baraujo25]

HLS gains an optional “Start from live edge” path for live/EVENT playlists. Segment durations are handled with sub-second precision where it matters for pacing and live-edge calculations.

Motivation:

• Long EVENT playlists always started from the first listed segment; load tests for live-like behavior need a live-edge-aligned starting point (RFC 8216–style window from the end of the playlist).
• Precision: Whole-second truncation in duration reporting and playlist parsing skewed timing and edge calculations.

Changes:

• New checkbox in the sampler UI (disabled when MPEG-DASH protocol is selected; tooltip states it applies to live/EVENT only).
• Persisted on com.blazemeter.jmeter.hls.logic.HlsSampler and exposed through VideoStreamingSampler for the streaming implementation.
• HlsSampler: When enabled on a non-VOD playlist with no prior segment, skip older segments so playback starts near the live edge, using three target durations of media time from the latest segments (RFC 8216 Section 6.3.3 style). Resume behavior continues from the last played segment.
• Playlist: EXTINF durations converted with Math.round to milliseconds; added getTargetDurationSeconds() for live-edge thresholding.