feat: INSERT without column names, generated PRIMARY KEY in INSERTs

[levkk]

• feat: support INSERT statements without column names for sharding, e.g. INSERT INTO sharded VALUES ($1, $2) #insert
• feat: inject pgdog.unique_id() as the primary key when it's not specified in an INSERT statement
• fix: pgdog.unique_id() not working with EXPLAIN

[codecov]

Codecov Report

❌ Patch coverage is 96.05096% with 31 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...rontend/router/parser/rewrite/statement/auto_id.rs	94.08%	22 Missing ⚠️
pgdog/src/admin/set.rs	0.00%	5 Missing ⚠️
pgdog/src/frontend/router/parser/statement.rs	98.71%	2 Missing ⚠️
pgdog/src/backend/schema/mod.rs	88.88%	1 Missing ⚠️
...rontend/router/parser/rewrite/statement/visitor.rs	75.00%	1 Missing ⚠️

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