NATS .NET v3.0.0-preview.11

Last planned preview on the 3.0 line centered on OpenTelemetry: a new NATS.Client.OpenTelemetry package, richer metrics, and lower-overhead tracing. Also moves the socket connection interfaces into NATS.Client.Abstractions and tightens the header-parsing hot path.

OpenTelemetry:

• Add OpenTelemetry package (#1172)
• Add custom span destination name formatter (#1201)
• Add ack/dropped metrics and collapse inbox trace tags (#1194)
• Exclude NATS status frames from consumed metrics (#1195)
• Make shared instrumentation options thread-visible (#1207)
• Match subject filters without per-message allocation (#1206)
• Fix null-key tag in receive fallback (#1205)

Core & packaging:

• Move socket connection interfaces to NATS.Client.Abstractions (#1192)
• Add abstractions package boundary test (#1197)
• Optimize header handling with SearchValues (#1203)
• Simplify object store base64url encoder (#1199)
• Gate positive-path test connections with ConnectRetryAsync (#1198)
• Remove stale net6.0 references (#1196)

Thanks to @colprog for the custom span destination name formatter (#1201) and the SearchValues header optimization (#1203).

Thanks to everyone testing the previews so far. This should be the last one; please give it one more round of testing, and if no bugs turn up we'll cut the stable 3.0 release in about a week.

Full Changelog: v3.0.0-preview.10...v3.0.0-preview.11