generic channel support for FlightClient

[rumenov]

Allow FlightServiceClient to be parameterized over the underlying channel type, so
users can wrap a tonic channel with custom interceptors or services.

Motivation: Annotating outbound Flight requests with metadata (e.g. injecting
OpenTelemetry trace context into headers) currently requires forking or wrapping at
a higher level. Making the channel generic lets callers compose tower
layers/interceptors idiomatically and propagate distributed tracing context without
bespoke plumbing.

[alamb]

Thank you @rumenov -- I think this is technically an API change (as now FlightClient is templated) but a good one.

I think we should move the test and ensure CI is passing, but then this looks good to me

We are preparing a new major release with API changes soon. see here for more details

• #9110

[rumenov]

Thank you @rumenov -- I think this is technically an API change (as now FlightClient is templated) but a good one.

I think we should move the test and ensure CI is passing, but then this looks good to me

We are preparing a new major release with API changes soon. see here for more details

• Release arrow-rs / parquet Major version 59.0.0 (May 2026) #9110

Thanks for the review!

It is an API change but it is not a breaking API change. Everything should keep working as before

[alamb]

The MSRV failure is unrelated to this PR. For more details:

• msrv check failing on main due to tonic@0.14.6 #9938

[alamb]

The CI failure is not due to your changes (your changes just triggered the rebuild) so I'll just merge this PR in and we can sort out any additional failures as a follow on PR