Fix datetime parameter formating bug

[alex-clickhouse]

Previously, when we wanted to preserve an instant we would simply send the number of ticks in UTC. That would get interpreted as UTC no matter what the column type, thus making everything consistent. There's a problem with this, however:

This is fine:

curl "http://localhost:8123/?param_dt=1705320000" -d "INSERT INTO test.datetime_test VALUES ({dt:DateTime})"

But this throws:

curl "http://localhost:8123/?param_dt=0" -d "INSERT INTO test.datetime_test VALUES ({dt:DateTime})"

Code: 41. DB::Exception: Cannot parse DateTime: value 0 cannot be parsed as DateTime for query parameter 'dt': at row 0: While executing ValuesBlockInputFormat. (CANNOT_PARSE_DATETIME) (version 25.12.1.649 (official build))

This means that values near the epoch won't work, hence the bug reported here: #183

This PR changes the http parameter formatting approach to use strings instead, with the appropriate timezone adjustments based on the parameter type to maintain consistent behavior. Also adds a bunch more tests.

---

Note

Fixes DateTime HTTP parameter formatting

• Switches HttpParameterFormatter to emit ISO strings for DateTime/DateTime64, converting UTC/Local values into the parameter’s target timezone (or UTC) while sending Unspecified as-is
• Adds helpers FormatDateTimeInTargetTimezone and FormatDateTime64InTargetTimezone for timezone-aware ISO formatting

Extensive test coverage added

• New tests for HTTP params and bulk copy covering Unspecified, Utc, Local, and DateTimeOffset across UTC, Europe/Amsterdam, and no-timezone columns
• Validates instant preservation vs wall-clock semantics, with/without timezone hints in parameter types
• Regression tests for Unix epoch (0) and min range, plus DateTime64 sub-second precision handling

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[Copilot]

Pull request overview

This PR fixes a bug where DateTime parameters formatted as Unix timestamps near epoch (e.g., 0 for 1970-01-01 00:00:00) were rejected by ClickHouse's HTTP parameter parser. The fix changes HTTP parameter formatting to use ISO-formatted strings with appropriate timezone conversions instead of Unix timestamps.

Changes:

• Modified HttpParameterFormatter.cs to format DateTime/DateTime64 parameters as ISO strings with timezone conversions instead of Unix timestamps
• Added comprehensive test coverage for DateTime/DateTime64 parameter handling across different timezones, DateTimeKind values, and edge cases including Unix epoch

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
ClickHouse.Driver/Formats/HttpParameterFormatter.cs	Replaced Unix timestamp formatting with ISO string formatting and timezone conversion logic for DateTime/DateTime64 parameters
ClickHouse.Driver.Tests/Types/TimezoneHandlingTests.cs	Added extensive test coverage for DateTime/DateTime64 parameter handling, timezone conversions, and edge cases including Unix epoch