revert: "feat(RUN-1013): Adjust max number of cached sandboxes" (#2184)

This reverts commit 75c57bc.

As canister executions increase, it's essential to maintain more spawned
sandboxes to accelerate sandbox executions. While the original change
reduced memory usage to switch to the memory-based allocator, production
metrics indicate minimal risk.

Author: berestovskyy

rs/config/src/embedders.rs

@@ -48,7 +48,7 @@ pub(crate) const DEFAULT_MIN_SANDBOX_COUNT: usize = 500;
 
 /// Sandbox process eviction ensures that the number of sandbox processes is
 /// always below this threshold.
-pub(crate) const DEFAULT_MAX_SANDBOX_COUNT: usize = 1_000;
+pub(crate) const DEFAULT_MAX_SANDBOX_COUNT: usize = 2_000;
 
 /// A sandbox process may be evicted after it has been idle for this
 /// duration and sandbox process eviction is activated.