Refactor HashTableOpenAddressingBase: consolidate API and enhance docs (#1317)

Remove insert/hasKey/add aliases in favor of put/containsKey directly,
add ConcurrentModificationException check in iterator's next(), remove
redundant iterator remove(), and expand class-level and inline
educational commentary explaining open addressing, tombstones, probe
chains, and lazy relocation.

Co-authored-by: Claude Opus 4.6 <[email protected]>

Author: williamfiset