fix(bigframes): Fix bugs compiling ambiguous ids and in subqueries

[TrevorBergeron]

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Fixes #<issue_number_goes_here> 🦕

[gemini-code-assist]

Code Review

This pull request introduces several updates, including adding a fillna(False) to isin operations, refactoring BigQuery query generation to use explicit table aliasing (_bf_source), and adjusting the SQL parser to handle table aliases before time travel clauses. Feedback suggests qualifying the wildcard selector in BigQuery queries for consistency and warns that the parser change might cause regressions for SQL dialects that expect aliases after table samples.

[gemini-code-assist]

To maintain consistency with the qualified column selection in the if block and to further prevent ambiguity when this query is used as a subquery, consider qualifying the wildcard selector as well.

Suggested change

	select_clause = "SELECT *"
	select_clause = "SELECT _bf_source.*"

[gemini-code-assist]

Moving the alias parsing to the top of _parse_table correctly addresses BigQuery's syntax requirements (where the alias precedes the FOR SYSTEM_TIME AS OF clause). However, this change unconditionally parses the alias before the table sample, which may break dialects that set ALIAS_POST_TABLESAMPLE = True. Since this is a vendored parser, if it's intended to support multiple dialects, consider making this move conditional on the dialect's settings or ensuring that the alias can still be parsed after the sample if needed.