Add RegexPhraseQuery, PhrasePrefixQuery, ExistsQuery and EmptyQuery

[CharlesNg35]

This PR adds Node.js bindings for four Tantivy query types that are available in tantivy 0.25.0 but were not
yet exposed:

• RegexPhraseQuery — phrase search where each term is a regex pattern, with slop and max_expansions support
• PhrasePrefixQuery — phrase search where the last term is treated as a prefix, with max_expansions support
• ExistsQuery — matches all documents that have a non-null value in a given field
• EmptyQuery — matches no documents (useful as a placeholder/default)

Changes

• src/query.rs — Rust implementations for all four query types
• index.d.ts — TypeScript declarations
• test/index.spec.ts — Tests for the new queries (including error cases)

Usage examples

  // Fuzzy phrase matching: "apocal*" near "10" with slop
  Query.regexPhraseQuery(schema, 'content', ['apocal.*', '10'], 25)

  // Autocomplete: "apocalypse di" → matches "apocalypse divine", "apocalypse dix"
  Query.phrasePrefixQuery(schema, 'content', ['apocalypse', 'di'])

  // Filter: only documents that have a value in "category"
  Query.existsQuery(schema, 'category')

  // No-op placeholder
  Query.emptyQuery()

Note
This code was generated with the help of Claude Claude. Please review the Rust implementations.

Closes #27