Catch the branch up with dev (45 commits) so testers can run the perf work
against current dev.
Conflict resolutions:
- downloaders/requests.py: keep the branch's racing-gated read1, adaptive
controller speed reporting and byte-range slice guards; take dev's
content-encoding checks (raw reads are skipped on an encoded body) and its
rolling SpeedWindow for the no-controller speed fallback. The single-URL
ranged-parallel gate now requires no speed limit and no caller Range.
- service.py / session.py: keep the branch's TimeoutHTTPAdapter and retry
config, raise POOL_MAX_SIZE to 64 so dev's pool-starvation fix survives
(pool_block=True stalls threads on a pool smaller than the in-flight count).
- docs: dev split configuration.md into per-area pages, so the branch's rnet
network option rows moved to reference/configuration/network.md.
subtitle.language_priority and audio.language_priority prepend to the CLI
languages, so the named languages sort first and nothing is filtered.
--exact-lang now applies to the sorts too, through matching_languages, which
follows the same RFC 4647 rule as Tracks.by_language and ignores invalid tags.
Document tvdb_api_key, tvdb_pin, tvdb_order and metadata_providers, the
--tvdb and --tvdb-order flags with their behaviour when an order does
not cover a whole series, the new REST API parameters, and the Matroska
TVDB2 tag prefixes.
One CPython interpreter caps sustained segment throughput at ~160 MB/s;
spawned children each run the existing thread-pool path on a contiguous
chunk of the batch, reaching NIC line rate on fast CDNs. Opt-in via
--download-processes (default 1), engaged only for 24+ segment batches.
Sessions are rebuilt per child from a picklable spec; RnetSession falls
back to a single process when it has no impersonate preset.
imSp4rky