[METRICS SDK] Synchronous instruments with drop aggregation must behave as no-op

[dbarker]

Background:

The sync instrument benchmarks measure recording latency when instruments are disabled (created from a disabled meter) and when drop aggregation is configured through a view. The results show instruments with drop aggregation produce significantly higher latency than a disabled instrument (See #4470 (comment)).

Instrument	Disabled	Drop Aggregation	Overhead vs. Disabled
Counter (threads:1)	0.223 ns	181 ns	812x
Counter (threads:2)	0.334 ns	336 ns	1006x
Counter (threads:4)	0.335 ns	548 ns	1636x
Histogram Explicit (threads:1)	0.215 ns	180 ns	837x
Histogram Explicit (threads:2)	0.215 ns	198 ns	921x
Histogram Explicit (threads:4)	0.227 ns	556 ns	2450x

The drop aggregation path can be optimized to behave like a no-op instrument and avoid the costly attribute hashing and thread synchronization.

Scope:

(edit)

1. Update the SDK meter to not create storage for a view with Drop aggregation
2. Update tests to cover configuring drop aggregation with a single instrument view and catch-all views

1. Add a boolean flag (and public const accessor) to SyncWritableMetricStorage that is set to true if drop aggregation is configured.
2. For each Record method of SyncMetricStorage and SyncMultiMetricStorage return early (before taking any locks) if drop aggregation is configured.

Related spec requirements:

An instrument should behave as a no-op if the meter is disabled or if all views of the instrument resolve to drop aggregation.

https://opentelemetry.io/docs/specs/otel/metrics/sdk/#instrument-enabled
https://opentelemetry.io/docs/specs/otel/metrics/sdk/#drop-aggregation

If a Meter is disabled, it MUST behave equivalently to No-op Meter.

The value of enabled MUST be used to resolve whether an instrument is Enabled. See Instrument Enabled for details.

The synchronous instrument Enabled MUST return false when either:

• Status: Development - The MeterConfig of the Meter used to create the instrument has parameter enabled=false.
• All resolved views for the instrument are configured with the Drop Aggregation.