fix(config): clean per-format outDir when using object format

[Kyujenius]

• This PR contains AI-generated code, but I have carefully reviewed it myself. Otherwise, my PR may be closed.

Description

With format: { esm: { outDir: 'esm' }, cjs: { outDir: 'cjs' } } and clean: true, the per-format directories are never cleaned. resolveClean runs once against the root outDir at src/config/options.ts:150 and the result is shared across every resolved config via ...config — per-format outDir overrides applied later in the map at L346-358 never make it into that array, so cleanOutDir only globs the root directory.

Deferring resolveClean into the per-format loop gives each config its own clean array derived from that format's effective outDir. A user-supplied per-format clean (overrides?.clean) wins over the top-level one, and overrides.outDir is resolved to an absolute path in the same place to keep override semantics consistent with the root outDir.

Linked Issues

fixes: #843

Additional context

The new test in tests/clean.test.ts fails without the fix and passes with it — it checks that stale files in each per-format outDir get removed and that the build still writes new output into the same directories. All existing clean tests still pass; if you don't use per-format outDir overrides, nothing changes — each resolved config still gets resolveClean(true, outDir, cwd) against the shared root outDir and produces the same [slash(outDir)] as before.

validateSea never reads clean, so its parameter type is narrowed to Omit<ResolvedConfig, 'clean' | 'format'>. This keeps the intermediate config object type accurate once clean moves out.

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commit: 8055d3a