Add streaming support for reading rows from Bigtable

[nrempel]

Add streaming support for reading rows from Bigtable

This PR adds streaming support for reading rows from Bigtable, allowing for more efficient processing of large result sets by streaming results as they arrive rather than waiting for the complete response.

Key Changes

1. Added new streaming methods to BigTable:

   • stream_rows() - Stream results from a standard row query
   • stream_rows_with_prefix() - Stream results from a prefix-based query

2. Added new dependency:

   • futures-util = "0.3.31" to both bigtable_rs and examples crates

3. Implemented streaming support in read_rows.rs with decode_read_rows_response_stream()

4. Added a new example demonstrating streaming usage in examples/src/stream.rs

Benefits

• More memory efficient for large result sets by processing rows as they arrive
• Allows processing to begin before all results are received
• Maintains consistent timeout handling with existing non-streaming methods
• Preserves existing row parsing logic that is tested through conformance tests

Note on Streaming and H2 Flow Control

The implementation leverages Tonic's H2 backpressure handling to create end-to-end flow control: consumers request data via try_next(), which pulls from Tonic only when ready, allowing the server to throttle based on client capacity. This native H2 flow control is particularly well-suited for Bigtable's variable-sized result sets and processing times, providing memory efficiency and network resilience without additional complexity.

Example Usage

The new streaming API allows for processing results as they arrive:

❯ cargo run --package examples --bin stream
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.08s
     Running `target/debug/stream`
------------
key1
    [cf1:c1] "value1.v1" @ 1730754124325000
    [cf1:c1] "value1" @ 1730754120003000
------------
key2
    [cf1:c1] "value2" @ 1730754153781000
    [cf1:c1] "value2" @ 1730754120242000
------------
key3
    [cf1:c1] "value3" @ 1730754120486000

[nrempel]

Alright, removing the timeout parameter + 'a lifetime made things a lot nicer.

What do you think?

[paulodiovani]

Just one suggestion and LGTM.
Hope the author likes it too. :)

[liufuyang]

Thanks again, I think it looks great, just some minor comments above, if you have time to fix, otherwise I can merge it and release another version later.

[nrempel]

Done! Thanks for the prompt review 👍🏻

[nrempel]

🥳

If you're able to publish a release to crates.io, we'll be using this feature shortly :)

[liufuyang]

@nrempel Thanks. I pushed in 0.2.15 just now.