Fix memory access violation in partition_with_ram_budget

[ninjaasmoke]

• Does this PR have a descriptive title that could go in our release notes?
• Does this PR add any new dependencies?
• Does this PR modify any existing APIs?
  • Is the change to the API backwards compatible?
• Should this result in any changes to our documentation, either updating existing docs or adding new ones?

Reference Issues/PRs

What does this implement/fix? Briefly explain your changes.

Fixes a potential crash in partition_with_ram_budget function when k_base parameter exceeds the number of partitions created.

Issue:
When the partitioning algorithm creates fewer partitions than the requested k_base value, the code attempts to access cluster centers that don't exist, leading to memory access violations and crashes.

Example error (intermittent):

Processing global k-means (kmeans_partitioning Step)
Residuals unchanged: 175.863 becomes 175.863. Early termination.
ERROR: k (5) > num_center(3)
unknown location(0): fatal error: memory access violation at address: 0x20ebdbf40: no mapping at fault address

This occurs when k_base=5 is passed but the k-means algorithm converges to only 3 clusters, causing out-of-bounds access in the cluster size estimation step. The issue is intermittent due to the non-deterministic nature of k-means clustering.

Solution:
Added a bounds check to ensure k_base never exceeds the actual number of partitions:

k_base = std::min(k_base, static_cast<size_t>(num_parts));

This prevents out-of-bounds access during cluster size estimation while preserving the intended functionality.

Any other comments?

This is a minimal, safe fix that maintains backward compatibility. The change ensures robust behavior when the partitioning algorithm determines that fewer partitions are needed than initially requested via k_base.

[ninjaasmoke]

@gopalrs Review please?