feat: add flags to specify a custom runtime.

[ielashi]

Problem

To enable running canbench without flakiness in the ic repo, it is desirable to able to specify a path for the runtime (pocket ic) to use. canbench didn't provide that flexibility, as it always downloads the runtime from the network.

Solution

Add two flags, one to set the path to the runtime, and another to skip the hash verification step altogether.

[github-actions]

canbench 🏋 (dir: examples/fibonacci)

No significant performance changes detected ✅

examples/fibonacci/canbench_results.yml is up to date ✅

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Benchmark: fibonacci_20
  total:
    instructions: 2224 (no change)
    heap_increase: 0 pages (no change)
    stable_memory_increase: 0 pages (no change)

---------------------------------------------------

Benchmark: fibonacci_45
  total:
    instructions: 3011 (no change)
    heap_increase: 0 pages (no change)
    stable_memory_increase: 0 pages (no change)

---------------------------------------------------

[github-actions]

canbench 🏋 (dir: examples/btreemap_vs_hashmap)

No significant performance changes detected ✅

examples/btreemap_vs_hashmap/canbench_results.yml is up to date ✅

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Benchmark: insert_users
  total:
    instructions: 2.57 B (no change)
    heap_increase: 871 pages (no change)
    stable_memory_increase: 0 pages (no change)

---------------------------------------------------

Benchmark: remove_users
  total:
    instructions: 2.07 B (no change)
    heap_increase: 0 pages (no change)
    stable_memory_increase: 0 pages (no change)

---------------------------------------------------

Benchmark: pre_upgrade_bench
  total:
    instructions: 743.98 M (-0.00%) (change within noise threshold)
    heap_increase: 519 pages (no change)
    stable_memory_increase: 184 pages (no change)

  serialize_state (scope):
    instructions: 729.04 M (-0.00%) (change within noise threshold)
    heap_increase: 519 pages (no change)
    stable_memory_increase: 0 pages (no change)

  writing_to_stable_memory (scope):
    instructions: 14.93 M (no change)
    heap_increase: 0 pages (no change)
    stable_memory_increase: 184 pages (no change)

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