fix(pg-delta): order leading enum value additions

[pjpjq]

Summary

Fixes #304.

• schedule pending enum label additions until an adjacent label already exists in the simulated working enum
• emit leading inserted runs from right to left, e.g. b BEFORE c then a BEFORE b
• keep existing middle/edge addition behavior covered with regression controls

RED evidence

Before the fix:

• enum.diff produced a BEFORE b before b existed for source ('c') -> target ('a','b','c')
• the new PG17 integration regression failed with 22023: "b" is not an existing enum label

Validation

• bun run --cwd packages/pg-delta test src/core/objects/type/enum/enum.diff.test.ts
• PGDELTA_SKIP_DUMMY_SECLABEL_BUILD=1 PGDELTA_TEST_POSTGRES_VERSIONS=17 TESTCONTAINERS_RYUK_DISABLED=true bun run --cwd packages/pg-delta test --retry=0 --test-name-pattern "add multiple leading enum values before the first existing value" tests/integration/type-operations.test.ts
• PGDELTA_SKIP_DUMMY_SECLABEL_BUILD=1 PGDELTA_TEST_POSTGRES_VERSIONS=17 TESTCONTAINERS_RYUK_DISABLED=true bun run --cwd packages/pg-delta test --retry=0 tests/integration/type-operations.test.ts
• bun run format-and-lint
• bun run check-types
• bun run knip

Note: I also attempted PGDELTA_SKIP_DUMMY_SECLABEL_BUILD=1 PGDELTA_TEST_POSTGRES_VERSIONS=17 TESTCONTAINERS_RYUK_DISABLED=true bun run test:pg-delta; it hit unrelated local Testcontainers/Postgres connection timeouts in non-enum integration files, so I stopped it after confirming the targeted enum coverage and project checks above.

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🦋 Changeset detected

Latest commit: a06f8da

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@supabase/pg-delta	Patch

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