This commit adds the ability to convert snowflakes [MERGE INTO](https://docs.snowflake.com/en/sql-reference/sql/merge) functionality into a functional equivalent implementation in duckdb.
To do this we need to break apart the WHEN [NOT] MATCHED syntax into separate statements to be executed indepedently.

This commit only adds the transform, there is more refactoring required in fakes.py in order to handle a transform
that transforms a single expression into multiple expressions.

* main:
  chore(main): release 0.9.20 (tekumara#115)
  fix: $$  not considered a variable
  fix: concurrent connection write-write conflict
  refactor: extract test_connect.py
  feat: SHOW PRIMARY KEYS for table (tekumara#114)
  chore(main): release 0.9.19 (tekumara#113)
  feat: Implements basic snowflake session variables via SET/UNSET (tekumara#111)
  chore(deps-dev): bump pyright from 1.1.366 to 1.1.369 (tekumara#112)
  chore(main): release 0.9.18 (tekumara#110)

Got basic case for merge working with a merge2 function, needs to be cleaned up, deleting original merge, fix result statement.

* main:
  fix: Only set variables for SetItem expressions (tekumara#116)

* main:
  feat: alter table cluster by
  chore: cruft update
  chore: bump sqlglot 25.5.1

* main: (38 commits)
  feat(server): support time & timestamp types
  ci(server): description - cover more types
  feat(server): handle snowflake ProgrammingError
  refactor: use rowtype for sf metadata in arrow schema
  feat(server): support empty result set
  chore(main): release 0.9.24 (tekumara#128)
  fix: don't require pandas at import time
  chore(main): release 0.9.23 (tekumara#126)
  feat: support conn.is_closed()
  refactor: extract conn, cursor, pandas_tools
  refactor: describe_as_rowtype uses sf_type
  refactor: describe_as_rowtype
  refactor: extract describe_as_result_metadata
  feat(server): support cur.description
  feat(server): support bool, int, float types
  chore(main): release 0.9.22 (tekumara#124)
  wip(server): add /queries/v1/abort-request
  fix: fetchmany supports irregular sizes
  fix: column types for DESCRIBE
  feat: describe view information_schema.*
  ...

* main:
  chore(deps): update ruff requirement from ~=0.5.1 to ~=0.6.3 (tekumara#130)
  chore(deps-dev): bump pyright from 1.1.374 to 1.1.378 (tekumara#133)

This reverts commit dfa68e1.

because it doesn't work when the alias is for a select expression

eg: tekumara#24 (comment)