feat(rust/ffi): implement ErrorFromArrayStream on the driver exporter

[fornwall]

What

The exported driver left the ADBC 1.1.0 ErrorFromArrayStream slot as None
(rust/ffi/src/driver_exporter.rs, previously a TODO). That slot is the
mechanism a consumer uses to recover the full AdbcError — status, vendor
code, structured details — when a result stream fails mid-iteration. Without
it, everything a Rust driver attaches to its adbc_core::error::Error during
streaming is reduced to an errno + message string for any foreign driver
manager (the error is wrapped in ArrowError::ExternalError, and arrow-rs's
FFI_ArrowArrayStream only carries the Display string across FFI).

How

• Wrap every exported reader (LastErrorReader) so that whenever iteration
  yields an ArrowError::ExternalError carrying an adbc_core::error::Error,
  the full error is stashed in a shared slot.
• Back each exported stream with ExportedArrayStreamPrivateData, which
  delegates schema/array export to an inner arrow-produced stream and keeps the
  last-error slot reachable.
• Implement ErrorFromArrayStream to materialize an FFI_AdbcError from the
  retained Error (reusing the existing TryFrom<Error> / ErrorPrivateData
  machinery) and write the ADBC status. The returned error is owned by the
  stream and released with it, matching the ADBC contract that the pointer is
  valid until the next call or stream release.

Testing

• New test_error_from_array_stream drives the exported C driver directly
  (the Rust driver manager imports streams via arrow's ArrowArrayStreamReader,
  which has no notion of this ADBC-specific entry point) and asserts message,
  status, vendor code, sqlstate and structured details all survive.
• The dummy driver gains a STREAM_ERROR_QUERY trigger to produce a
  mid-stream failure.
• Verified clean under Miri (no UB, no leaks) across the full
  stream+error lifecycle. Full adbc_dummy suite and cargo build --workspace
  pass.

Relationship to apache#4475 / apache/arrow-rs#10300

This is the natural complement to apache#4475:
that PR fixes the error code (mapping Status::Cancelled → ECANCELED
instead of the arrow-rs catch-all EINVAL); this PR recovers the error
object. Both extract the adbc_core::error::Error from the
ArrowError::ExternalError source chain, so if apache#4475 lands first (introducing
its custom exported_stream.rs), these should be reconciled: the last-error
retention here would fold into that custom stream's private data rather than
layering a second wrapper on top of FFI_ArrowArrayStream::new.

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