GH-35975: [Go] Support importing decimal256

[lidavidm]

Rationale for this change

We didn't implement this type.

What changes are included in this PR?

We now import this type. (And handle some other error cases.)

Are these changes tested?

Yes.

Are there any user-facing changes?

Yes.

• Closes: [Go] C Data Interface can't import decimal256 #35975

[ursabot]

Benchmark runs are scheduled for baseline = 9dd4c52 and contender = 5e5002d. 5e5002d is a master commit associated with this PR. Results will be available as each benchmark for each run completes.
Conbench compare runs links:
[Finished ⬇️0.0% ⬆️0.0%] ec2-t3-xlarge-us-east-2
[Finished ⬇️0.59% ⬆️0.0%] test-mac-arm
[Failed ⬇️0.33% ⬆️0.0%] ursa-i9-9960x
[Finished ⬇️0.24% ⬆️0.03%] ursa-thinkcentre-m75q
Buildkite builds:
[Finished] 5e5002de ec2-t3-xlarge-us-east-2
[Finished] 5e5002de test-mac-arm
[Failed] 5e5002de ursa-i9-9960x
[Finished] 5e5002de ursa-thinkcentre-m75q
[Finished] 9dd4c525 ec2-t3-xlarge-us-east-2
[Finished] 9dd4c525 test-mac-arm
[Finished] 9dd4c525 ursa-i9-9960x
[Finished] 9dd4c525 ursa-thinkcentre-m75q
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