feat: add memory allocation tracker

[ScriptedBro]

Summary

Adds memory allocation tracking and reporting for contract execution to help developers understand memory footprint and optimize usage.

What changed

• Hooked memory tracking into contract execution in ContractExecutor::execute
• Captures memory growth snapshots at key execution stages
• Tracks:
  • total allocation count
  • total bytes allocated
  • peak memory usage
  • top 5 largest tracked allocations
• Displays a memory allocation summary section after execution
• Includes memory_summary in JSON output for run --json
• Added unit tests for memory tracking totals/peak/top-allocation ordering

Acceptance Criteria

• Allocation count tracked correctly
• Peak memory usage displayed
• Top 5 allocations listed
• Memory summary shown in output
• Included in JSON output

Validation

• cargo test inspector::budget:: --lib
• Manual verification with:
  • soroban-debug run --contract tests/fixtures/wasm/counter.wasm --function increment
  • soroban-debug run --contract tests/fixtures/wasm/counter.wasm --function increment --json

Notes

• "Top 5 allocations" reports up to 5 tracked allocation events (checkpoint-based memory growth deltas). Small contracts may show fewer than 5 entries.

Closes #203

Issue: #203