[WIP] feat(rust): Let the returned RecordBatchReader outlive & parameters

[felipecrv]

This is a draft PR showing a problem with the annotations of functions that return impl RecordBatchReader and take & paramemeters.

The first commit shows how I work around it. When I try to make a Box'd RecordBatchReader, the compiler complains because there is a possibility that the impl RecordBatchReader returned might be holding any of & passed in the parameters:

When I'm forced to be explicit about lifetimes, I end up with:

struct BoxedReaderConnection(DummyConnection);

impl BoxedReaderConnection {
    pub fn get_objects<'a>(
        &'a self,
        depth: ObjectDepth,
        catalog: Option<&'a str>,
        db_schema: Option<&'a str>,
        table_name: Option<&'a str>,
        table_type: Option<Vec<&'a str>>,
        column_name: Option<&'a str>,
    ) -> Result<Box<dyn RecordBatchReader + Send + 'a>> {
        let reader = self.0.get_objects(
            depth,
            catalog,
            db_schema,
            table_name,
            table_type,
            column_name,
        )?;
        let boxed_reader: Box<dyn RecordBatchReader + Send + 'a> = Box::new(reader);
        Ok(boxed_reader)
    }
}

This is not ideal because I don't want to tie the lifetime of table_name: Option<&'a str> to the lifetime of the returned RecordBatchReader.

So I believe the proper solution is to change the adbc_core traits to explicitly declare that the RecordBatchReader can outlive the input references. Like this:

    fn get_objects<'a>(
        &'_ self,
        depth: options::ObjectDepth,
        catalog: Option<&'_ str>,
        db_schema: Option<&'_ str>,
        table_name: Option<&'_ str>,
        table_type: Option<Vec<&'_ str>>,
        column_name: Option<&'_ str>,
    ) -> Result<impl RecordBatchReader + Send + 'a>;

allowing a wrapper that boxes the RecordBatchReader to be written as

impl BoxedReaderConnection {
    pub fn get_objects<'a>(
        &'_ self,
        depth: ObjectDepth,
        catalog: Option<&'_ str>,
        db_schema: Option<&'_ str>,
        table_name: Option<&'_ str>,
        table_type: Option<Vec<&'_ str>>,
        column_name: Option<&'_ str>,
    ) -> Result<Box<dyn RecordBatchReader + Send>> {
        let reader = self.0.get_objects(
            depth,
            catalog,
            db_schema,
            table_name,
            table_type,
            column_name,
        )?;
        let boxed_reader = Box::new(reader);
        Ok(boxed_reader)
    }
}