Initial DataChunk API support

[taniabogatsch]

This PR introduces a new DataChunk API. See the discussion here. Ideally, all interaction between go-duckdb and duckdb's data chunks eventually goes through this API without compromising performance. As an outlook, in #219, I further used this API for go-duckdb's scanner.

As a first step, this PR moves all interaction between the Appender and data chunks to the DataChunk API and its setter functions, further decreasing the complexity of the Appender code.

This PR adds the following functions:

• func (chunk *DataChunk) InitFromTypes(ptr unsafe.Pointer, types []C.duckdb_logical_type) error
• func (chunk *DataChunk) Destroy()
• func (chunk *DataChunk) SetSize() error
• func (chunk *DataChunk) SetValue(colIdx int, rowIdx int, val any) error

Additionally, I reverted the column index in the data chunk when returning an unsupported type error message to 0-based indexing.

Questions

• I introduced a new helper.go file. However, I recommend renaming this file or moving its functions to a different place. What do you think?
• The DataChunk, and by implication, the vector structs are becoming universal components without ties to the Appender. Thus, I renamed appender_vector.go to vector.go. Also, I added a new file, vector_setters.go, to create some functionality separation and decrease file sizes. Is this a good approach?

[ajzo90]

Nice! A few suggestions on the public interface.

Perhaps InitFromTypes and SetSize should be private methods (for now)? InitFromTypes because it's using internal arguments and SetSize since it's likely not necessary to expose publicly?

Destroy can also be private until we have cases where it needs to be public. If/when it goes public I think the signature should be Close() error to follow go naming conventions.

[taniabogatsch]

@ajzo90, good call, I've made them private. Do you have any other suggestions?

[JAicewizard]

Small question, is there a reason projection support wasn't added? If not could this still be added via another PR? and if yet should we make a new type to support projection?

[JAicewizard]

Also for table functions SetSize is must be exposed, as a tablefunction might not want to fill the entire chunk, I will expose this in my PR. (Same for GetSize)

[JAicewizard]

Sorry I am just reviewing this now, I wasn't aware of the PR and didn't have any time to review this week. In the case these need to be fixed, maybe a fix PR would be appropriate?