v0.4.0

The headline of this release is fs2.nats.micro — typed NATS micro services
implementing ADR-32.
Alongside it, another round of hot-path work landed across core pub/sub, JetStream,
and Object Store, and 0.4 starts a new binary-compatibility series.

Micro services (fs2.nats.micro)

• An endpoint is described once as a plain Rpc[P, I, E, O] value — subject pattern
  with typed captures, request payload, typed error, response payload — and interpreted
  on both sides: rpc.handle(...) inside a NatsService, Micro(client).call(rpc)(...)
  from the caller. Definitions can live in a shared module (#57)
• Subject patterns are checked at compile time: pattern["orders.*"].bind[OrderId]
  rejects malformed literals, computes the capture arity, and binds captures through
  TokenCodecs (String, Int, Long, UUID, or your own)
• Payloads via Payload.empty / bytes / string / json[A] (jsoniter-scala),
  with optional schema text published in the endpoint INFO metadata
• Errors are typed end to end: handlers return F[Either[E, O]], errors travel as
  ADR-32 error headers and come back as Left(E) at the caller — transport failures
  are the only thing raised in F
• Full ADR-32 discovery: every instance answers $SRV.PING / INFO / STATS in all
  nine subject forms with the standard response types, so nats micro CLI tooling
  works out of the box; per-endpoint stats are also available locally via
  NatsService#stats
• Instances load-balance through a queue group by default; service and endpoint
  metadata per ADR-33; request headers are visible to handlers, and response headers
  can be set via Reply

The module ships inside the fs2-nats artifact and adds no new dependency
(jsoniter-scala was already on the classpath for JetStream). See
docs/micro.md
for the full tour.

Performance

• Dialled sockets now set TCP_NODELAY, removing Nagle-induced latency (up to
  ~40 ms per round trip) from request/reply; socket options are configurable via
  the new TransportConfig.socketOptions (#44)
• JetStream.publishAsync — and Object Store put / KV putAsync on top of it —
  no longer starts a supervised fiber per message; correlation is registered up
  front and the reply completes on the shared inbox drain fiber (#47)
• Request correlation moved from four CAS loops over an immutable-map Ref to a
  ConcurrentHashMap plus AtomicLong, so pipelined request/reply scales instead
  of contending on one serialization point (#49)
• Subscription lookup on the delivery path uses a primitive-keyed LongMap and a
  single volatile read instead of boxing the sid and reading two Refs per
  message (#50)
• JetStream API replies are decoded in place in a single jsoniter pass instead of
  a payload copy plus two passes per PubAck (#51)
• Object Store put feeds SHA-256 by wrapping each chunk's backing arrays instead
  of flattening them, dropping the extra full copy of all object data on the way
  to the wire (#53)

Compatibility

• 0.4 starts a new early-semver series: not binary compatible with 0.3.x,
  recompile against 0.4.0. Source-level, typical users need no changes
• TransportConfig gained a socketOptions field (default: TCP_NODELAY on for
  sockets the library dials — override socketOptions to opt out). Named-argument
  construction is unaffected; only full-arity positional construction needs the
  new argument
• The NatsClient trait gained a package-private abstract method, so hand-written
  implementations of the trait outside fs2.nats (e.g. test stubs) no longer
  compile — delegate to a real client instead
• Scala 3, cats-effect 3.7, fs2 3.13; JDK 11+
• Dependency refresh: jsoniter-scala 2.38.17 → 2.40.1; munit 1.3.5, sbt 1.12.15,
  scalafmt 3.11.5 (test/build-scoped only)

What's Changed

• Minor & major updates by @ThatScalaGuy in #39
• Test library updates by @ThatScalaGuy in #37
• Patch updates by @ThatScalaGuy in #38
• Patch updates by @ThatScalaGuy in #40
• Minor & major updates by @ThatScalaGuy in #41
• Test library updates by @ThatScalaGuy in #43
• Add fs2.nats.micro: typed NATS micro services (ADR-32) by @ThatScalaGuy in #57

Full Changelog: v0.3.1...v0.4.0