Support columns with variable partitions in Rust's send_column api

[Wumpf]

Both Python & C++ APIs have ways of partitioning a component column arbitrarily to e.g. log point clouds in a single send_columns call.
Rust however, right now only supports partitions of length 1 for each element (i.e. at each timestep you end up with an array of length 1) which is still great for the usecase of sending e.g. Scalar, but not the full picture.

Note that the lower level send_chunk API that the Rust recording stream comes with has none such restrictions (and is what is used by Python and C++).

[teh-cmc]

If it's not outright blocked by, it would at the very least heavily benefit from:

• Eager/early serialize of components to arrow in Rust and C++ #7245

which needs to happen multi-datatype tagged components anyhow.

[teh-cmc]

Somewhat related, the Rust definition of send_columns seems wrong not optimal:

    pub fn send_columns<'a>(
        &self,
        ent_path: impl Into<EntityPath>,
        timelines: impl IntoIterator<Item = TimeColumn>,
        components: impl IntoIterator<Item = &'a dyn re_types_core::ComponentBatch>,
    ) -> RecordingStreamResult<()> {

Why take an iterator of ComponentBatches instead of the more flexible AsComponents?