feat: re-write date/time functions (calls + DEFAULT) in omni inserts

[jkaczman]

When we perform an INSERT into an omnisharded table, right now, the functions within the statement (or COLUMN_DEFAULT in the table schema) are executed separately on each shard. In the case of time/date functions, this means that they will drift slightly apart, as their execution time will not be the exact same.

To fix this, this PR re-writes all those time/date functions (Postgres ref), specifically: current_date, current_time, current_timestamp, clock_timestamp, localtime, localtimestamp, now, statement_timestamp, timeofday, and transaction_timestamp.

It handles both calls within a VALUES list, as well as is compatible with functions specified within COLUMN_DEFAULT in the table schema. It's also compatible with simple protocol, extended protocol, and prepare/execute.

Refactoring

• Pushed TransactionType into a Transaction type, so that the time the transaction started could be saved for use with now() / other functions that rely on transaction start time.
• Created a PreparedPlan type to encapsulate everything the PreparedStatement cache stores for Prepare statements (instead of passing around separate fields in a tuple).
• Pushed GeneratedId and its corresponding parameter number into a GeneratedParam type.

Shortfalls:

• If the client specified a timezone, it only works with strings like "UTC" and "America/New_York"; Postgres supports other types such as INTERVAL '-08:00' HOUR TO MINUTE. Right now it errors to prevent incorrect behavior falling through. We previously didn't support any kind of timezone parsing whatsoever.

Docs: pgdogdev/docs#114.
Helm: pgdogdev/helm#140.
Fixes #1521.

[codecov]

Codecov Report

❌ Patch coverage is 95.15279% with 46 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...ntend/router/parser/rewrite/statement/timestamp.rs	89.57%	34 Missing ⚠️
pgdog/src/frontend/client/mod.rs	81.81%	2 Missing ⚠️
pgdog/src/frontend/client/query_engine/query.rs	77.77%	2 Missing ⚠️
...rc/frontend/router/parser/rewrite/statement/mod.rs	93.93%	2 Missing ⚠️
...router/parser/rewrite/statement/simple_prepared.rs	97.61%	2 Missing ⚠️
pgdog/src/frontend/client/query_engine/discard.rs	83.33%	1 Missing ⚠️
...rc/frontend/client/query_engine/end_transaction.rs	87.50%	1 Missing ⚠️
...gdog/src/frontend/prepared_statements/statement.rs	93.33%	1 Missing ⚠️
pgdog/src/frontend/router/parser/cache/ast.rs	88.88%	1 Missing ⚠️

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[levkk]