fix(minMax): select dates in one pass without temporary arrays

[OskarEichler]

Fixes and simplification

• Select the minimum/maximum in a single pass, skipping absent values during selection instead of allocating a filtered copy.
• Pass the existing arguments object directly, avoiding a second temporary array for variadic calls.
• Return null consistently when every supplied value is absent. Previously dayjs.max([null, undefined]) returned undefined, while dayjs.max([]) returned null.
• Replace overlapping empty-input conditions with the naturally empty selection result.

Valid result identity, first-winner tie handling, ignored falsy entries, and invalid-date propagation are preserved. Input arrays are not mutated. This builds on the null-skipping behavior introduced in #2330.

Compatibility

No new API, types, dependencies, or runtime requirements. The observable correction is null instead of undefined for all-absent input; callers explicitly distinguishing those values should account for it. Invalid Day.js objects are still propagated, not silently ignored.

Verification

• 6,002 source equivalence/empty-input checks, comparing against baseline across array/variadic calls, frozen/sparse arrays, ties, null/falsy inputs, and multiple invalid dates.
• All 794 existing tests / 93 suites and 100% line coverage on the reviewed patch set, including independent locale/calendar fixes; release 1.11.23 backport suite also passes.
• Lint, all 40 declarations, complete builds, and size limit pass.
• A synthetic nullable 100,000-entry array benchmark (100 selections) measured 128.93 ms before and 124.64 ms after. This is not an application-wide speedup claim; the main benefit is removing temporary arrays and a traversal.

No tests were added or changed. Legacy size checking used a process-local OpenSSL compatibility flag on Node 22, not a package change.