feat: always dump separate constraint with name

[tianzhou]

Fix #83

[Copilot]

Pull Request Overview

This PR introduces always-named constraint mode for pgschema, fixing issue #83 where explicitly named constraints were being converted to inline syntax during dumping. The change ensures all constraints are dumped as table-level with explicit names, preserving constraint names and improving schema consistency.

Key changes:

• Modified constraint generation to always use named table-level format (e.g., CONSTRAINT users_pkey PRIMARY KEY (id))
• Updated both CREATE TABLE and ALTER TABLE statements to use consistent constraint naming
• Added support for preserving complex foreign key attributes (DEFERRABLE, NOT VALID)

Reviewed Changes

Copilot reviewed 129 out of 129 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
internal/diff/table.go	Refactored constraint handling to generate all constraints as table-level with explicit names
internal/diff/constraint.go	Updated constraint SQL generation to always include constraint names
internal/diff/identifier_quote_test.go	Updated test expectations to match new named constraint format
cmd/dump/dump_integration_test.go	Added integration test for issue #83
testdata/dump/issue_83_explicit_constraint_name/*	Added test case data for named constraint preservation
Multiple testdata files	Updated expected outputs to reflect new constraint naming format

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