gRPC transport for `milvus-clj.client`. Wraps `io.milvus/milvus-sdk-java`.

Responsibilities:
  - Build a MilvusServiceClient from config (the `open` fn).
  - Implement `IMilvusCore` + `IMilvusAdmin` + `IMilvusExtras` via a
    `GrpcClient` defrecord that holds the service client and its own
    config for lifecycle.
  - Translate ex-info-tagged errors for `client/classify-error`.

Keepalive defaults are tuned for fragile intermediaries (tailscale
userspace netstack, cloud NAT). `keepAliveWithoutCalls(true)` is the
critical bit: without it gRPC only pings during active RPCs, so idle
clients die silently with
`UNAVAILABLE: Keepalive failed. The connection is likely gone`.

This ns is loaded lazily via `requiring-resolve` from
`milvus-clj.client/make`, so the gRPC Java SDK classes are only
loaded when the gRPC transport is actually selected.

HTTP/REST transport for `milvus-clj.client`. Talks Milvus v2.5.x REST API
on port 19530 (yes, the same port as gRPC — Milvus 2.5+ multiplexes via
the proxy) via `java.net.http.HttpClient` + `clojure.data.json`.

PORT GOTCHA: do NOT use 9091. That's the metrics/health endpoint and
returns `404 page not found` on every REST API call. Milvus 2.5+ serves
gRPC and the v2 REST API on the SAME port (19530) via the proxy.

Why this exists:
  - HTTP/1.1 with short-lived connections has zero idle state; the
    gVisor netstack idle-sweep (see `transport/grpc.clj` for the gory
    details) cannot kill a connection that doesn't outlive a request.
  - `java.net.http` is the repo's standard HTTP client (see
    `hive-mcp/src/hive_mcp/embeddings/openrouter.clj` for the canonical
    pattern).

NOTE on `Connection: close`: java.net.http explicitly rejects the
`Connection` header as restricted (throws `IllegalArgumentException`).
The JDK's HTTP/1.1 client manages connection reuse internally and the
default pool's idle timeout is short; combined with our per-record
client lifetime (one `with-client` scope), idle-state exposure is
negligible. If a deployment sees gVisor-class idle kills even on
HTTP, the mitigation is to open a fresh `HttpClient` per request —
trivial to add later by moving builder construction into `http-post`.

Implements `IMilvusCore` + `IMilvusAdmin`. `IMilvusExtras` methods throw
— hive-milvus doesn't call them and PR-2 scope forbids gold-plating.

Return shapes are LSP-equivalent to `transport/grpc.clj` — every
protocol method here produces the same keyword-keyed map shape as the
gRPC `do-*` helpers, so a conformance suite can swap transports
transparently.

Loaded lazily via `requiring-resolve` from `milvus-clj.client/make`.