More FlightEndpoint attributes

[EnricoMi]

Rationale for this change

What changes are included in this PR?

Are these changes tested?

Are there any user-facing changes?

[github-actions]

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See also:

• Other pull requests
• Contribution Guidelines - Contributing Overview

[adamreeve]

Just some minor comments and I'm not a cython expert but it looks good to me 👍

[adamreeve]

I'm curious why the template parameter isn't needed here, but I guess it's inferred from the constructor parameter type and/or count return type?

[EnricoMi]

Thanks for the code review, raised upstream: apache#43537.