fix: add missing insert_format/bulk_insert_format to PostgresGrammar

[bedus-creation]

Summary

PostgresGrammar was missing insert_format() and bulk_insert_format(), which BaseGrammar._compile_bulk_create() depends on. Seeders running against the Postgres grammar crashed with:

AttributeError: 'PostgresGrammar' object has no attribute 'bulk_insert_format'

The MySQL, SQLite, and MSSQL grammars all define these methods — Postgres was the only one missing them.

Changes

Added both methods to PostgresGrammar (after delete_format()), mirroring the SQL used by the other grammars:

• insert_format() → INSERT INTO {table} ({columns}) VALUES ({values})
• bulk_insert_format() → INSERT INTO {table} ({columns}) VALUES {values}

Testing

• Verified both methods resolve and return the expected format strings.
• Existing test suite unaffected (one file changed, two methods added).

[bedus-creation]

🔴 Review verdict: CHANGES REQUESTED — DO NOT MERGE

(Posting as a comment; a formal "request changes" review is blocked because the PR author and reviewer share the same GitHub account in this setup.)

Verified ✅

• insert_format() → INSERT INTO {table} ({columns}) VALUES ({values}) — matches MySQL/SQLite/MSSQL exactly.
• bulk_insert_format() → INSERT INTO {table} ({columns}) VALUES {values} — matches MySQL/SQLite/MSSQL exactly.
• Diff touches only PostgresGrammar.py (6 insertions); no other grammar files changed.
• Non-DB suite passes locally: 1493 passed, 7 skipped, 0 failed (live-Postgres DB tests excluded per project convention).

Blocking ⛔

• No regression test. This was an AttributeError crash on Postgres bulk insert that shipped precisely because nothing exercised these methods. A unit test asserting both format strings on PostgresGrammar is required before approval.

Non-blocking nit 💅

• Other grammars order insert_format → bulk_insert_format → delete_format; here they were added after delete_format. Cosmetic only — moving them above keeps grammars consistent.

Please push the follow-up commit with the unit test; I will re-review.