[BUG]: `MultiThreadedExecutor` in the driver where a single-threaded one would do

[advaypakhale]

Issue Description

main() in waterlinked_dvl_driver.cpp uses MultiThreadedExecutor, but as written it does not seem to do anything over a single-threaded one. More of a simplification than a bug?

waterlinked_dvl/waterlinked_dvl_driver/src/waterlinked_dvl_driver.cpp

Line 308 in 78eb226

rclcpp::executors::MultiThreadedExecutor executor;

• All the node callbacks are created without a callback group (L232-L284), so they share the node's default mutually-exclusive group. A MultiThreadedExecutor will not run them concurrently anyway.
• By default all LifecycleNode callbacks are registered under the default callback group too.

So I believe a SingleThreadedExecutor would behave the same here and possibly provide some performance gains over a MultiThreadedExecutor.

Steps to Reproduce

N/A

Expected Behavior

Either use SingleThreadedExecutor since it is equivalent here, or, if concurrent in-flight commands were intended, set up reentrant or separate callback groups so the multithreading actually does something.

Error Message

Runtime Environment

Not environment specific

Additional Context

No response