feat:Add final DSL support so no rawsql needed for docs

[ankitml]

Ticket(s) Closed

Expands SQLAlchemy query DSL coverage so docs/examples no longer need raw SQL fallbacks for key search cases.

• Adds tokenizer-cast support (tokenizer=) to search.match_all, search.match_any, search.term, and search.phrase.
• Adds constant scoring support (const=) to match_all, match_any, term, phrase, and regex; adds boost= support to regex.
• Adds search.exists(field) helper for idiomatic field @@@ pdb.exists().
• Extends search.range_term() to support scalar point queries (e.g. range_term(field, 1)) in addition to existing range-literal mode.
• Extends search.phrase() to support pretokenized token arrays (Sequence[str]) with optional slop.
• Fixes array+slop runtime casting edge case by coercing token arrays to TEXT[] before ::pdb.slop(...) (avoids psycopg VARCHAR[] cast failure).

What

Why

How

Tests