fix: treat unsupported SQL plans as "not implemented"

[crepererum]

Which issue does this PR close?

--

Rationale for this change

Use the correct error type because API users may rely on that (e.g. to generate appropriate HTTP error codes).

What changes are included in this PR?

Change some errors from Internal to NotImplemented.

Are these changes tested?

SQL test, see changed test.

Are there any user-facing changes?

Improved error types.

[andygrove]

LGTM

[alamb]

I think this is great -- I believe that @tustvold had some opinions on these codes

[tustvold]

I believe that @tustvold had some opinions on these codes

Did I? 😅 If I did, I don't remember 😆 Looks good to me

Edit: Oh I remember, I wanted to adjust the typing to remove this from being a possibility, but I don't mind this approach either

[ursabot]

Benchmark runs are scheduled for baseline = 1ec2a83 and contender = 379cf39. 379cf39 is a master commit associated with this PR. Results will be available as each benchmark for each run completes.
Conbench compare runs links:
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on ec2-t3-xlarge-us-east-2] ec2-t3-xlarge-us-east-2
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on test-mac-arm] test-mac-arm
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on ursa-i9-9960x] ursa-i9-9960x
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on ursa-thinkcentre-m75q] ursa-thinkcentre-m75q
Buildkite builds:
Supported benchmarks:
ec2-t3-xlarge-us-east-2: Supported benchmark langs: Python, R. Runs only benchmarks with cloud = True
test-mac-arm: Supported benchmark langs: C++, Python, R
ursa-i9-9960x: Supported benchmark langs: Python, R, JavaScript
ursa-thinkcentre-m75q: Supported benchmark langs: C++, Java