No LINQ translation for DateTime members and methods

## Problem

The provider translates no `DateTime` members and no `DateTime` methods. Only a direct comparison works.

EF Core's base `RelationalMemberTranslatorProvider` registers no built-in translators. It adds plugins only (`RelationalMemberTranslatorProvider.cs:22`). `ClickHouseMemberTranslatorProvider` adds `ClickHouseArrayMethodTranslator` and `ClickHouseStringMethodTranslator` only. No date/time translator exists.

## Measured behaviour

Tested against a real ClickHouse server, on a `DateTime` property with column type `DateTime64(6, 'UTC')`:

| Expression | Result |
| --- | --- |
| `.Year` `.Month` `.Day` `.Hour` `.Minute` | `InvalidOperationException: The LINQ expression ... could not be translated` |
| `.Date` `.DayOfWeek` `.DayOfYear` `.TimeOfDay` | same |
| `.AddDays(1)` `.AddMonths(1)` | same |
| `DateTime.UtcNow` / `DateTime.Now` / `DateTime.Today` | same |
| `dt - dt` (result is `TimeSpan`) | `InvalidCastException: Unable to cast object of type 'System.TimeSpan' to type 'System.DateTime'` |
| `ts > new DateTime(2020, 1, 1)` | works: ``WHERE `d`.`ts` > '2020-01-01 00:00:00.000000'`` |

The `dt - dt` result is different from the others. It gives an `InvalidCastException` instead of a clear "could not be translated" message. This looks like a defect, not only a missing feature.

## Suggested work

Add one shared date/time member translator. Give it the CLR type as a parameter so that it serves `DateTime`, `DateOnly`, and `DateTimeOffset` from the same class. Npgsql uses this shape (`NpgsqlDateTimeMemberTranslator`).

ClickHouse functions to map:

| Member | ClickHouse function |
| --- | --- |
| `.Year` | `toYear` |
| `.Month` | `toMonth` |
| `.Day` | `toDayOfMonth` |
| `.Hour` | `toHour` |
| `.Minute` | `toMinute` |
| `.Second` | `toSecond` |
| `.DayOfYear` | `toDayOfYear` |
| `.DayOfWeek` | `toDayOfWeek` (note: ClickHouse counts Monday as 1, .NET counts Sunday as 0) |
| `.Date` | `toStartOfDay` |
| `.AddDays` / `.AddMonths` / `.AddYears` | `date_add` |
| `DateTime.UtcNow` | `now64` |

Also translate the `DateTime` difference to `date_diff`, or give a clear "not supported" message.

Take care with two ClickHouse behaviours:

- `toDayOfWeek` starts at Monday = 1. .NET `DayOfWeek` starts at Sunday = 0. The translation must adjust the value, in the same way the string translators adjust the 0-based to 1-based index.
- These functions read the column timezone. For a `DateTimeOffset` property the result must stay consistent with the UTC instant that the column holds.

## Notes

Found while I investigated #53. `DateTimeOffset` needs the same translators, so one shared class is better than a `DateTimeOffset`-only class. #53 itself needs comparison support only, which already works.

Start with ClickHouseMemberTranslatorProvider and RelationalMemberTranslatorProvider.cs:22, then compare NpgsqlDateTimeMemberTranslator with the existing ClickHouseArrayMethodTranslator and ClickHouseStringMethodTranslator. Verify the listed DateTime mappings against ClickHouse behavior, including DayOfWeek numbering and DateTimeOffset timezone consistency. Done also requires DateTime differences to translate or fail with a clear unsupported message.

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