[IMPROVEMENT] Add Linux throughput benchmarking guide and helper script

[ObaidAbdullah16]

In raising this pull request, I confirm the following (please check boxes):

Reason for this PR:

• This PR adds new functionality.
• This PR fixes a bug that I have personally experienced or that a real user has reported and for which a sample exists.
• This PR is porting code from C to Rust.
• Other (documentation / developer tooling improvement)

Sanity check:

• I have read and understood the contributors guide.
• I have checked that another pull request for this purpose does not exist.
• If the PR adds new functionality, I've added it to the changelog. If it's just a bug fix, I have NOT added it to the changelog.
• I am NOT adding new C code unless it's to fix an existing, reproducible bug.

Repro instructions:

N/A — this PR does not change extraction logic and does not fix a specific bug. It adds documentation + a helper script for repeatable Linux throughput benchmarking.

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Summary

This PR adds a small Linux-focused benchmarking guide plus a helper script to measure CCExtractor throughput (MB/s) in a repeatable way.

The goal is to make it easier for contributors to compare performance before/after changes (scheduler, I/O, filesystem, build flags, etc.) using a consistent workflow.

Context

I’m working towards Linux throughput/performance tuning work and wanted to contribute a small prerequisite: a repeatable way to benchmark CCExtractor throughput before/after changes.

Changes

• Add docs/performance/linux-throughput.md with a short, repeatable throughput benchmarking workflow for Linux.
• Add tools/bench_linux_throughput.sh to run CCExtractor multiple times and print wall time + MB/s, with optional CSV output.
• Link the guide from README.md under a new Performance section.

Sample / verification instructions (Linux)

This PR is docs + tooling (not a bug fix), but to make the instructions concrete here is a public sample you can use to try the script:

Sample (public/open movie):

• Big Buck Bunny (Blender Foundation): https://peach.blender.org/download/

Example run:

# 1) Build CCExtractor so ./ccextractor exists in the repo root.
# 2) Download a Big Buck Bunny MP4 file from the link above (any resolution is fine)
#    and set INPUT to that file path.

export INPUT="/path/to/big_buck_bunny.mp4"
export OUTDIR="/tmp/ccx_bench_out"
mkdir -p "$OUTDIR"

bash tools/bench_linux_throughput.sh --input "$INPUT" --runs 3 --outdir "$OUTDIR" --csv "$OUTDIR/results.csv"

Expected result:

• The script prints per-run seconds and MB/s.
• results.csv is created with columns run,seconds,mb,mb_per_s.

[ObaidAbdullah16]

Hi @cfsmp3 — could you please take a look when you have a moment? This PR adds a Linux throughput benchmarking guide + helper script. Thanks!

[cfsmp3]

Closing — we appreciate the effort, but we don't want to add benchmarking tooling to the project at this time. The README whitespace changes are cosmetic and not needed. Thanks though.