[FlightSQL] SQLite example pulls GPL-licensed modernc.org/ccorpus into all consumers' go.sum

[laurentgo]

Describe the enhancement requested

The modernc.org/sqlite dependency (and its transitive chain: modernc.org/ccgo,
modernc.org/ccorpus — a 105 MB package embedding GCC test-suite C source files
licensed under the GPL) is a direct root-module dependency solely because of the
FlightSQL SQLite example package. This forces every downstream consumer of arrow-go
to include those packages in their go.sum and triggers warnings from automated
license-scanning tools (FOSSA, OSS Review Toolkit, etc.), even when they never
import any example code.

Proposal: move arrow/flight/flightsql/example/ into its own Go sub-module
(github.com/apache/arrow-go/v18/arrow/flight/flightsql/example). The two test
files that use the SQLite server as a backend (sqlite_server_test.go,
driver/driver_test.go) would move with it, and a go.work would be added for
local development. pkg.go.dev shows zero external importers of the example package
on v18.

Component(s)

Other

[laurentgo]

Looks like I did my analysis wrong based on an older version of sqlite, but current version of sqlite used by the arrow repo has the gcc test suite stripped already.

Not sure if there's much value to this work unless we think it's still desirable to not have sqlite showing up as a root dependency

[zeroshade]

I don't think it's a huge issue given that the compiler will drop it from any binary that importing arrow-go which isn't compiling the example. So the only real issue is that it would show up as a development download during dev. So I think I can close this for now unless someone runs into an issue and legitimately needs it to not be in the root go.mod. Thanks for looking into though aand confirming!