⚡ Verify DeflateEncoder optimization and add benchmark

[404Setup]

This PR verifies the performance optimization for DeflateEncoder in src/stream.rs.

Analysis:
The task was to replace resize(bound, 0) with try_reserve + unsafe { set_len } in DeflateEncoder to avoid zero-filling overhead. Upon inspection, this optimization was already present in the codebase.

Verification:

• Created benches/encoder_perf.rs to measure DeflateEncoder throughput.
• Baseline (Optimized): ~16.3ms (~612 MiB/s) for 10MB input.
• Unoptimized (Reverted locally): ~17.6ms (~566 MiB/s).
• Improvement: ~8% faster with the optimization.

Other Changes:

• Attempted to apply similar optimization to DeflateDecoder, but reverted it because reading into an uninitialized &mut [u8] slice is Undefined Behavior in stable Rust.
• Applied cargo clippy fixes to src/stream.rs (modernizing io::Error construction).

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PR created automatically by Jules for task 2045398248251583668 started by @404Setup

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