fix: bin date_bin month strides outside chrono's range

[ThilakShekharShriyan]

Which issue does this PR close?

Closes #25855.

Rationale for this change

date_bin with a month stride returned NULL for timestamps that sit outside DateTime<Utc>, even when the month start still fits in the output type. Second, millisecond, and microsecond timestamps can be wider than chrono's range. A month bin should be NULL only when that bin itself does not fit.

What changes are included in this PR?

The narrow month path is unchanged and still uses chrono for timestamps that fit in i64 nanoseconds.

The wide path, used when the nanosecond conversion overflows, now bins on the civil calendar with the same day-count conversion date_trunc already uses. It keeps the existing stride rule, including negative strides, and clamps a missing day to the end of the month the way checked_add_months does. When the candidate is after the source, it steps back one stride from the origin rather than from the already-clamped date.

A result that does not fit the output unit is still NULL. That covers Timestamp(Second)::MIN and a nanosecond source with a stride too large for i64 nanoseconds.

What is the testing strategy for this PR?

• date_bin_errors.slt covers the issue: 10_000_000_000_000 seconds bins to month start 9999998294400, and the negative input bins to -10000001059200.
• The same file updates the large millisecond stride from issue date_bin() panics on large inputs #20219. That bin fits in milliseconds (-4306016287785600000) and used to be NULL only because chrono overflowed. The nanosecond form of that stride still expects NULL.
• A unit test checks that the wide path matches the chrono path for in-range values, including month-end clamping, a leap day, negative strides, and dates before the epoch.

Are there any user-facing changes?

Yes. Month-stride date_bin now returns the month start for timestamps outside chrono's range when that instant fits the output type. Values that already fit in i64 nanoseconds are unchanged. No public API change.

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