Expand query DSL with CTEs, windows, pattern matching, and broader join support

[elcritch]

Summary

This PR extends the Ormin query DSL with several common SQL features and improves
test coverage around the newer syntax.

Added DSL features

• CTE support via:

  query:
    with recent(select Post(id, author) where id <= 3)
    select recent(author)
  

• Window expressions via:

  over(row_number(), partitionby(author), orderby(id))

• Pattern predicates:

  • name like ?pattern
  • name ilike ?pattern
  • not (name \like ?pattern)

• Additional join keywords:

  • leftjoin, leftouterjoin
  • rightjoin, rightouterjoin
  • fulljoin, fullouterjoin
  • crossjoin
  • legacy outerjoin still accepted

Refactoring

• Generalized source/column handling so CTEs and base tables share the same
  column-resolution path.
• Reworked join rendering so explicit join aliases and CTE-backed sources behave
  consistently.

Tests and docs

• Added CTE tests:
  • single CTE
  • chained CTEs
  • CTEs used inside subqueries
• Added window-function tests:
  • row_number()
  • running sum(...)
• Added pattern-matching tests for like, ilike, and negated like
• Expanded join coverage in tests/tfeature.nim
• Updated README examples and supported-feature docs

Notes

• ilike is lowered portably on SQLite using lower(lhs) like lower(rhs).
• rightjoin / fulljoin are DSL-supported and compile-covered here, but not
  runtime-validated in the SQLite suite.