Optimize table fetches for explicit attribute lists via entries-search projection

[PatrykGala]

MR Summary

• Added a fast path in fetch_experiments_table and fetch_runs_table for cases where attributes is an exact list.
• Extended fetch_table() with exact_attribute_names and routed eligible requests through a single projected entries-search flow instead of the split label/definition/value pipeline.
• Refactored search pagination/setup into reusable helpers (_build_entries_search_params, _fetch_entries_with_projection) and introduced TableSearchEntry parsing for direct table-row construction.
• Added NEPTUNE_QUERY_ENTRIES_SEARCH_MAX_PROJECTION_ATTRIBUTES (default 1000) to cap projection size and keep fallback behavior for larger requests.
• Kept backward-compatible fallback path when fast-path conditions are not met.
• Added/updated unit tests to cover fast-path usage for experiments/runs and fallback behavior around projection limits.