feat: migrate ChannelPaginatorsOrchestrator to ChannelManager

[MartinCupela]

Summary

ChannelPaginatorsOrchestrator becomes ChannelManager, and the legacy src/channel_manager.ts is
deleted. One manager now holds N channel lists — each a ChannelPaginator — keeps them in sync through an
EventHandlerPipeline per event type, and arbitrates ownership when a channel matches several lists.

The rename is the easy half. The bulk of this PR is feature parity: the legacy manager still had
behavior the paginator stack did not, so those gaps were closed first and the deletion comes last.

What was ported

Ported	Why it mattered
Predefined-filter response metadata — query() requests withResponse: true and keeps predefined_filter verbatim; it drives local matching (buildMatchFilters) and ordering (effectiveSort)	For a list built from a server-stored filter, the client knew none of it. A message.new for an archived channel was ingested into a list the server filters to { archived: false }
Hidden channels — excluded from lists unless the filter constrains hidden; channel.hidden re-evaluates filters	Hidden channels stayed visible until a re-query. Legacy removed them outright, which would evict them from a { hidden: true } list — this keeps them
Offline-DB parity — full request as the cache key (read and write), first-page query deferred until the sync manager reports completion, WS-driven reorders persisted	Predefined-filter lists shared a wrong cache row; the sync branch was unreachable whenever the cache had data; live reordering never reached the cache
Query retries — retryCount is a paginator option and ChannelPaginator defaults to DEFAULT_QUERY_CHANNELS_RETRY_COUNT	Channel queries had silently stopped retrying
Channel identity from events — one getCidFromEvent helper for the cached lookup and the fetch	updateLists threw on events whose only identity is event.channel.cid; removeItem ignored them

Deliberately not ported, each with a reason in decisions.md:
state.initialized, pagination.isLoadingNext, abortInFlightQuery, the 10 named handler overrides,
allowNotLoadedChannelPromotionForEvent, members-based channel construction, and the promoteChannel
pinned-ordering rules.

Bugs found while porting

Each of these was pre-existing and is covered by a test that fails without the fix:

• sort setter dropped the comparator's resolvers — after any paginator.sort = …, last_message_at
  resolved to channel.data.last_message_at (undefined) instead of the message paginator's value, and
  equal sort values ordered non-deterministically. Comparator construction now goes through one
  buildSortComparator().
• retryCount was off by one — 3 meant 3 attempts / 2 waits; it now means 3 retries / 4 attempts,
  matching what the legacy manager's own tests asserted.
• removeItem handler read only event.cid — a channel.deleted whose cid arrives nested in
  event.channel was ignored, so the channel stayed in every list.
• describe.each(['channel.deleted', 'channel.hidden']) never ran the hidden case — all three cases
  dispatched a hardcoded channel.deleted, which is why the missing handler went unnoticed.
• Two flaky client.test.js tests — the fixture built ten "channels" sharing one cid with
  same-millisecond timestamps, so ordering hinged on random uuids (~5% failure rate).

Breaking changes

ChannelManager keeps its name but is a different class — code importing it still compiles, which is
the risky part. Full tables (state, methods, options, types, helpers) are in the new ## ChannelManager
section of v9-to-v10-migration-guide-methods.md, including a
worked replacement for promoteChannel and a v10-RC → final rename table. In short:

• state.channels / pagination / initialized / error → state.paginators, with list state on
  paginator.state (items, hasMoreTail, isLoading, lastQueryError).
• queryChannels() / loadNext() / setChannels() / setQueryChannelsRequest() / setOptions() /
  setEventHandlerOverrides() → paginator methods and the pipeline API.
• lockChannelOrder → paginatorOptions.lockItemOrder; abortInFlightQuery and
  allowNotLoadedChannelPromotionForEvent removed (the latter replaced by inserting the exported
  ignoreEventsForUnknownChannels at index: 0).
• buildFilters() is gone stack-wide → buildQueryFilters() (request + offline cache key) and
  buildMatchFilters() (local matching). ChannelQueryShape is now the queryChannels request itself.
• 16 legacy types and 9 utility exports removed (promoteChannel & friends).
• Behavioral: hidden channels excluded by default, retryCount semantics, offline cache re-keyed,
  sortComparator assignment no longer survives a sort change (use sortComparatorFactory),
  channel.updated / channel.truncated re-emit instead of no-op.