Remove benchmarks and simplify demo scrolling

[rafambn]

Remove all performance benchmark suites, dependencies, Gradle tasks, CI steps, scripts, and retained results. Keep unit tests and the 100% instruction and branch coverage requirement.

Remove the demo's benchmark section and old design artifacts. Use normal page scrolling instead of a nested scrollbar, and synchronize the assembled demo output.

Validation:

• 186 JVM unit tests passed with no failures or skips.
• 100% instruction and branch coverage verification passed; HTML report generated.
• Library assemble and web demo assemble passed.
• No benchmark references or Gradle tasks remain.
• Desktop and mobile browser checks confirmed no inner scrollbar or horizontal overflow.