feat: expose Lance metrics via OpenTelemetry in Python and Node (#3609)

Bridges Lance's internal `metrics`-crate instrumentation (object store
request counts, bytes, latency, errors, and throttles) into
OpenTelemetry, in both the Python and Node bindings, with a shared
adapter in the Rust core. This is the LanceDB counterpart to
lance-format/lance#7537.

## Rust core (`rust/lancedb`)
Two new, **off-by-default** features:
- `metrics` — re-exports the [`metrics`](https://docs.rs/metrics) crate
as `lancedb::metrics` and turns on Lance's object-store instrumentation.
Install any `metrics`-compatible recorder to collect them.
- `metrics-otel` — adds `lancedb::metrics_otel`, a pull-based adapter
that installs a process-global recorder aggregating into lock-free
cumulative storage and exposes a snapshot/catalog API
(`register_metrics_recorder`, `metrics_catalog`, `snapshot_metrics`,
`MetricPoint`/`MetricValue`/`MetricKind`/`MetricDescription`). Both
bindings build on this.

## Python
`lancedb.otel.instrument_lancedb_metrics()` registers each metric as an
OpenTelemetry observable instrument on the given (or global)
`MeterProvider`. Available via the `otel` extra (`pip install
lancedb[otel]`), which pulls in only `opentelemetry-api` — the
application supplies and configures the SDK.

## Node
`instrumentLanceDbMetrics()` provides the equivalent wiring against
`@opentelemetry/api`. This is the only public entry point; the
underlying recorder/catalog/snapshot functions stay internal.

Because OpenTelemetry has no asynchronous histogram instrument,
histograms are exported Prometheus-style as `<name>_bucket` (with an
`le` attribute), `<name>_count`, and `<name>_sum`. Only `_sum` carries
the histogram's unit; `_bucket` and `_count` observe cumulative counts
and are unitless. The adapter is enabled by default in the Python and
Node builds, and off by default in the Rust crate.

## Notes
- Requires Lance ≥ `v9.0.0-beta.19`, which ships the object-store
metrics APIs (upstream lance-format/lance#7537, now merged). `main` is
already on beta.19, so this is a single feature commit with no
dependency bump.
- Tests: 8 Rust unit tests, 3 Python tests, 2 Node tests, all covering
the end-to-end object-store-metrics → OpenTelemetry path.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/src/js/functions/instrumentLanceDbMetrics.md

@@ -0,0 +1,42 @@
+[**@lancedb/lancedb**](../README.md) • **Docs**
+
+***
+
+[@lancedb/lancedb](../globals.md) / instrumentLanceDbMetrics
+
+# Function: instrumentLanceDbMetrics()
+
+```ts
+function instrumentLanceDbMetrics(meterProvider?): boolean
+```
+
+Register LanceDB metrics as OpenTelemetry observable instruments.
+
+Installs a process-global metrics recorder and creates one observable
+instrument per LanceDB metric (currently object store request counts, bytes,
+latency, errors, and throttles) on the given (or global) `MeterProvider`. The
+configured `MetricReader` then collects them on its own schedule.
+
+Counters and gauges map directly to observable counters/gauges. Because
+OpenTelemetry has no asynchronous histogram instrument, each histogram is
+exported Prometheus-style as cumulative `le` bucket counts (`<name>_bucket`,
+with an `le` attribute) plus `<name>_count` and `<name>_sum`.
+
+Requires `@opentelemetry/api` (a dependency) and, to actually export, an
+OpenTelemetry SDK such as `@opentelemetry/sdk-metrics`.
+
+## Parameters
+
+* **meterProvider?**: `MeterProvider`
+    The provider to register instruments on. Defaults to the
+    global provider from `@opentelemetry/api`.
+
+## Returns
+
+`boolean`
+
+`true` if the recorder is installed and instruments are registered.
+  `false` if a different `metrics` recorder is already installed in this
+  process (only one global recorder is permitted), in which case a warning is
+  emitted and no instruments are created. Calling this more than once is safe;
+  instruments are created only on the first successful call.

docs/src/js/globals.md

@@ -131,6 +131,7 @@
 - [RecordBatchIterator](functions/RecordBatchIterator.md)
 - [connect](functions/connect.md)
 - [connectNamespace](functions/connectNamespace.md)
+- [instrumentLanceDbMetrics](functions/instrumentLanceDbMetrics.md)
 - [makeArrowTable](functions/makeArrowTable.md)
 - [packBits](functions/packBits.md)
 - [permutationBuilder](functions/permutationBuilder.md)