Leios prototype recreation onto current main (chunked)

[ch1bo]

Note

The base branch here (leios-prototype) is the state before the recreation;
this PR is intended to merge by fast-forwarding leios-prototype to the head
of leios-prototype-remake. The diff is huge because it includes the
snapshot-merge to upstream main. For focused review:

• Recreation against current main: main...leios-prototype-remake
• Per-commit first-parent view: git log --first-parent ebc8eac0a8..leios-prototype-remake

Important

Cross-repo: this branch is consumed by ouroboros-consensus's
leios-prototype-remake (PR IntersectMBO/ouroboros-consensus#2041), where
the Leios threadnet test is currently green on 100/100 random seeds with
this branch pinned via SRP.

Done

• Snapshot-merge onto upstream main (ebc8eac0a8) — the
  leios-prototype-remake ref is reset to upstream main's tree while
  keeping the prototype's historic commits reachable via the merge
  commit's first parent.
• Demo-tuning: BearerBytes class replaces dataSize (55c16cf687)
  Drop the dataSize :: bytes -> Word field from ProtocolSizeLimits;
  replace with a class BearerBytes bytes where bearerBytesSize :: bytes -> Word and default instances for BS.ByteString, BL.ByteString,
  [Char], AnyMessage msg. The seven byteLimits* codec helpers no
  longer take a (bytes -> Word) argument; call sites drop the
  (fromIntegral . LBS.length) boilerplate. Driver.Limits gains a
  BearerBytes bytes constraint on the public entry points
  (runPeerWithLimits and friends).
• Demo-tuning: arrival-time Reception on recv + TraceRecvMsg
  (319743abd0) — bearer-side recv now returns Maybe (Reception a)
  where Reception a = MkReception !(IntMap Time) !a records per-chunk
  arrival times keyed by starting-byte offset, and that arrival time is
  threaded all the way through the decoder to surface on TraceRecvMsg :: Maybe Time -> AnyMessage ps -> TraceSendRecv ps (with TraceSendMsg :: Time -> AnyMessage ps -> ... for symmetry). The mux demuxer pairs each
  SDU's read time with its offset into the ingress queue
  (IngressQueueVal Int64 (IntMap Time) Builder). The driver's decoder
  threads (IntMap Time, Word rsz, Word sz) so the next-message arrival
  time isn't lost when a message boundary lands inside a chunk
  (runDecoderWithChannel_DecodeDone helper, mbEq <|> mbTm fallback).
  Reception is re-exported from Network.Mux and Ouroboros.Network.Mux;
  MonadMonotonicTime m propagates to a handful of test entry points.
  Squashes the prototype's original Reception drop together with the
  subsequent TraceRecvMsg consumer-side wiring + the four runDecoder*
  bugfixes that followed.
• Demo-tuning: field names on Reception (3afd70f505) — name the
  MkReception fields receivalTimes / received for ergonomic access.

Still TODO

• TCP_NOTSENT_LOWAT + TCP_NODELAY on socket bearer set on the
  mw/leios-prototype branch — can be rebased.
• Re-sign all commits if required for merge.
• Open question: can these add-ons be PRed straight upstream into
  ouroboros-network master, eliminating the need for a fork branch?

Intentional differences from the original prototype

The Leios mini-protocols (LeiosNotify, LeiosFetch) live in ouroboros-consensus
rather than here — easier iteration in one repo. That's why this branch carries
only the bearer-layer demo-tuning (arrival times, BearerBytes) but no Leios
protocol content.

Merge plan

Fast-forward leios-prototype to the head of this branch (after the
TODOs above are resolved).