fix: support Spark Connect sessions

[patrickswedish]

Summary

• dispatch Spark SQL functions and window expressions to the implementation matching the actual classic or Connect DataFrame/Column
• apply the same dispatch throughout SparkSQLCompare and its built-in array, boolean, numeric, and string comparators
• add regression coverage proving Connect expressions can be built without an active local SparkContext

Validation

• ruff check and ruff format --check on every changed Python file
• Spark Connect regression tests: passed
• Spark comparator and helper suite: 34 passed
• focused end-to-end SparkSQLCompare paths (merge, duplicate handling, mismatch reporting, windows, masking, and cache behavior): 8 passed

Closes #535

[fdosani]

Appreciate the PR. I've made some changes here: main...spark-connect-sessions. There are a few PRs in the pipeline which need reviewing, so appreciate the patients here. I've incorporated some of your design into this new standalone branch