v0.3.1 -- Performance improvements

Reduce allocations and overhead across core operators and concurrency primitives.

Changes

• PullFilter: filter in-place with Vec::retain instead of allocating a new Vec per chunk

• PullAndThen: reuse a persistent buffer across next_chunk calls, eliminating repeated heap allocations for filter_map operations

• par_eval_map: replace per-element oneshot channels with JoinHandles, removing one channel allocation per element. Decouple chunk pulling from task spawning via an intermediate VecDeque buffer.

• BroadcastReceiver: use Arc::try_unwrap to take ownership of shared chunks without cloning when the receiver holds the last reference

Cleanup

• Remove unused to_pascal_case function from pipe-macros
• Remove unused PipeError imports from cancel and meter modules
• Remove redundant name field from PullMeter