fix(bigquery)!: Support FORMAT_TIMESTAMP

[VaggelisD]

This PR adds support for BQ's FORMAT_TIMESTAMP through exp.TimeToStr:

bigquery> SELECT FORMAT_TIMESTAMP("%b-%d-%Y", TIMESTAMP "2050-12-25 15:30:55+00");
Dec-25-2050

snowflake> SELECT TO_CHAR(CAST(CAST('2050-12-25 15:30:55+00' AS TIMESTAMPTZ) AS TIMESTAMP), 'mon-DD-yyyy');
Dec-25-2050

duckdb> SELECT STRFTIME(CAST('2050-12-25 15:30:55+00' AS TIMESTAMP), '%b-%d-%Y');
┌───────────────────────────────────────────────────────────────────┐
│ strftime(CAST('2050-12-25 15:30:55+00' AS TIMESTAMP), '%b-%d-%Y') │
│                              varchar                              │
├───────────────────────────────────────────────────────────────────┤
│ Dec-25-2050                                                       │
└───────────────────────────────────────────────────────────────────┘

Regarding the changes in this PR:

1. For BQ, FORMAT_DATETIME was deduplicated from FORMAT_TIMESTAMP by introducing exp.TsOrDsToDatetime
2. For exp.cast(...), a bug was solved regarding the types_are_equivalent check; Note how get will either retrieve a str or a DataType.Type (the default value), so the comparison might be incorrect as stringifying DataTypes will prepend them with the Type.<type> enum prefix (e.g comparing Type.TIMESTAMP with DATETIME for DuckDB). To fix this we must retrieve either the TYPE_MAPPING or stringify the value of the enum type
3. For DuckDB, Type.DATETIME now maps to TIMESTAMP as these are aliases (this enables redundant cast eliminations from bullet 2)

Docs

BQ FORMAT_TIMESTAMP | DuckDB TIMESTAMP type | Snowflake TO_CHAR