MINOR: [Go] Normalize zero-length C Data buffers with regression coverage

[wangting0128]

Summary

• merge the zero-length C Data buffer normalization from fix(arrow/cdata): avoid unsafe.Slice on zero-length pointers #4
• make the regression test fail deterministically before the fix by checking that zero-length Go buffers do not retain the C sentinel pointer 0x1
• cover String, Binary, LargeString, and LargeBinary with all-null and all-empty values
• cover nested List<String> imports, empty StringView buffers, and the C stream -> record batch reader path used by Milvus

This targets milvus-io/milvus#52233, where compaction crashed in cimporter.importVariableValuesBuffer after a zero-length values buffer with address 0x1 was retained on a Go stack.

Verification

go test -tags test ./arrow/cdata
go test ./arrow/cdata
go test -tags test -run 'Test(StrArrayAllNulls|StrArrayEmptyValues|ListStringArrayAllNullChildValues|EmptyStringViewArbitraryZeroLengthPointer|RecordReaderStreamAllNullStrings)$' -count=100 ./arrow/cdata
go test -tags test -gcflags=all=-d=checkptr=2 -run 'Test(StrArrayAllNulls|StrArrayEmptyValues|ListStringArrayAllNullChildValues|EmptyStringViewArbitraryZeroLengthPointer|RecordReaderStreamAllNullStrings)$' -count=10 ./arrow/cdata

Negative-control verification was also performed: reverting only the sz == 0 guard makes the new tests fail consistently because the imported zero-length slice still has data pointer 0x1.

[github-actions]

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