Split benchmarks into individual targets

[preinlein]

What does this PR do?

Restructures the benchmarking system for lading_payload by:

1. Splitting the single default.rs benchmark entry point into individual standalone benchmarks
2. Reducing benchmark runtime by adjusting measurement times:
   • Setup benchmarks: 10 seconds with 1 second warm-up
   • Throughput benchmarks: 30 seconds with 1 second warm-up
   • Block operation benchmarks: 10 seconds with 1 second warm-up
3. Adding criterion_main! to each benchmark file to make them independently runnable

Motivation

This change improves the developer experience by:

• Allowing benchmarks to be run individually rather than all at once
• Reducing benchmark execution time from 90 seconds per benchmark to more reasonable durations
• Separating setup and throughput benchmarks with appropriate timing configurations

Additional Notes

The benchmark structure now follows a more modular approach where each payload type has its own dedicated benchmark file with appropriate measurement times. This makes it easier to run specific benchmarks during development and reduces the overall time needed for benchmark execution.

[preinlein]

• Example optimization hunt #1762
• Update hunt to use targetted benchmarks #1761
• Optimize benchmarks #1760
• Split benchmarks into individual targets #1759 👈 (View in Graphite)
• main

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[preinlein]

The stack can be validated by looking at the final Claude hunt results here: https://drive.google.com/file/d/1mbgFAFuC5s2HwM3IhoNCgqZcmt7Ho7a2/view?usp=sharing