fix: Elasticsearch online store - correctness, performance, and robustness fixes

[vanitabhagwat]

What this PR does / why we need it:

Fixes multiple bugs in the Elasticsearch online store:

• Wrong data served: online_read returned results in ES hit order instead of input entity key order, causing features to be assigned to wrong entities
• Silent data loss: No size param in ES query — only 10 results returned regardless of input size
• O(n²m) write performance: insert_values list rebuilt inside inner loop on every feature of every entity
• Frozen progress bar: progress callback never invoked during materialization
• Keyword search blocked: vector_enabled check rejected keyword-only queries in retrieve_online_documents_v2
• Bool type corruption: bool branch unreachable due to Python's bool subclassing int
• Timestamp parsing: Hardcoded strptime formats replaced with datetime.fromisoformat()
• Index existence guards: Added indices.exists() checks in update() and teardown()

Which issue(s) this PR fixes:

Misc