Update benchmarking docs and add ResNet results

[chloecrozier]

Numbers disagreed across the README, benchmarking pages, and tutorials.
Consolidates them onto one measured cross-host testbed.

Updated:

• Raw Ethernet, RoCE, and socket figures; every published row is loss-free
• README mirrors the benchmarking page, so they cannot diverge again

Added (requested in review):

• Five-model ResNet inference results
• Socket core scaling: TCP 52.0 -> 105.2 -> 108.5 Gb/s on 1/2/4 cores, replacing a table that showed 48% loss
• PCIe Gen5 x4 host attach (126 Gb/s), the ceiling behind every row

RTX PRO 6000 400 GbE benchmarks land in #162.

Test: mkdocs build --strict, check_doc_refs.py, check_html_links.py

[greptile-apps]

Greptile Summary

This PR consolidates DGX Spark benchmark documentation around measured cross-host results, adds five-model ResNet inference results, updates socket scaling data, and adds cross-host TCP/UDP example configurations.

Confidence Score: 5/5

The PR appears safe to merge with no outstanding review findings.

The previous socket core-count and missing cross-host configuration findings are resolved, and no accepted new issue remains.

Important Files Changed

Filename	Overview
docs/benchmarks/performance-dgx-spark.md	Updates the DGX Spark methodology and results for raw Ethernet, RoCE, TCP, UDP, and ResNet inference.
examples/socket_bench.cpp	Adds benchmark activity-window and receive-burst reporting used by the updated measurements.
examples/run_spark_bench.sh	Updates socket benchmark result collection and rate reporting.
README.md	Synchronizes headline benchmark and ResNet results with the detailed performance documentation.

_{Reviews (9): Last reviewed commit: "#251 - Update UDP cross-host benchmark r..." | Re-trigger Greptile}