feat(timestamp): improve ibis.timestamp()

[NickCrews]

• when you create a ibis.timestamp(), it detects the max needed resolution for that timestamp, and uses that. For example, "2025-04-17 01:02:03" before was infered as a dt.Timestamp with scale=None. Now it has scale=0, eg with second resolution. This sets the stage to allow for really big dates, like in the year 3000, to work. Otherwise, when a backend told to compile a Literal of type Timestamp(scale=None), it was forced to use the highest possible resolution to ensure that the result wasnt truncated. For eg datafusion, this meant it tried to cast to nanosecond resolution, but you can't fit these huge dates into nanosecond resolution.
• adds a nullable flag to the factory functions ibis.timestamp()
• adds typing to rules.highest_precedence_shape() and _dtype()
• makes them more ergonomic so you can pass in an iterable of other attribute names.
• adds .from_datetime and .from_pandas methods to dt.Timestamp, so the implementation is in one place

[github-actions]

ACTION NEEDED

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The commitlint output is:

⧗   input: fixup: fix timezone getting passed to Literal op
✖   type must be one of [build, chore, ci, depr, docs, feat, fix, perf, refactor, revert, style, test] [type-enum]

✖   found 1 problems, 0 warnings
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