chore: simplify migration memoize

[ferhatelmas]

What kind of change does this PR introduce?

chore

What is the current behavior?

There is a generic memoize utility for migration loading but its tests are testing it at all.

What is the new behavior?

It's used in one place, not needed. Drop it and its tests.

Additional context

Indirectly, it drops some any usage as well.

[Copilot]

Pull request overview

This PR removes an unused generic promise memoization helper from the migrations subsystem and replaces its only usage with a purpose-built cache for migration file loading.

Changes:

• Deleted memoizePromise utility and its (non-covering) tests.
• Implemented a directory-keyed in-module cache for loadMigrationFiles, including cache invalidation on rejection.
• Simplified lastLocalMigrationName() logic (explicit empty-migrations handling, and clearer “freeze at” lookup).

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/internal/database/migrations/memoize.ts	Removed unused promise memoization helper.
src/internal/database/migrations/memoize.test.ts	Removed tests that reimplemented memoization locally rather than testing the production helper.
src/internal/database/migrations/files.ts	Added a focused migration-files cache and adjusted callers to use it.

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[coveralls]

Coverage Report for CI Build 24467924764

Coverage decreased (-0.002%) to 82.471%

Details

• Coverage decreased (-0.002%) from the base build.
• Patch coverage: 3 uncovered changes across 1 file (22 of 25 lines covered, 88.0%).
• 1 coverage regression across 1 file.

Uncovered Changes

File	Changed	Covered	%
src/internal/database/migrations/files.ts	25	22	88.0%

Coverage Regressions

1 previously-covered line in 1 file lost coverage.

File	Lines Losing Coverage	Coverage
src/internal/database/migrations/files.ts	1	79.31%

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Coverage Stats

Relevant Lines:	33981
Covered Lines:	30492
Line Coverage:	89.73%
Relevant Branches:	7460
Covered Branches:	3685
Branch Coverage:	49.4%
Branches in Coverage %:	Yes
Coverage Strength:	349.02 hits per line

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💛 - Coveralls