fix(timezone): Make datetime usage timezone-aware for DTZ lint rules

[jenshnielsen]

• Use datetime.now(timezone.utc).astimezone() for local time with UTC offset
• Update all datetime.fromtimestamp() calls with tz parameter
• Store parameter cache timestamps as timezone-aware local time
• Parameter snapshot 'ts' field now includes UTC offset (e.g. '2024-01-01 13:00:00+01:00')
• Fix buggy manual timezone computation in AWG70000A driver
• Update all test files to use timezone-aware datetimes
• Update snapshot parsing to use fromisoformat() for ISO 8601 format

Fixes DTZ005, DTZ006, DTZ007 ruff lint violations. Existing datasets remain unaffected; only new ones have explicit timezone info.

[codecov]

Codecov Report

❌ Patch coverage is 95.65217% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 71.09%. Comparing base (a997230) to head (e6ff912).

Files with missing lines	Patch %	Lines
...rc/qcodes/instrument_drivers/Keysight/Infiniium.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #8355   +/-   ##
=======================================
  Coverage   71.09%   71.09%           
=======================================
  Files         305      305           
  Lines       31913    31903   -10     
=======================================
- Hits        22687    22681    -6     
+ Misses       9226     9222    -4     

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[Copilot]

Pull request overview

This pull request updates QCoDeS to use timezone-aware datetime values throughout the codebase to satisfy Ruff DTZ lint rules and to make newly produced timestamps unambiguous by including a UTC offset where appropriate (while continuing to store datasets as POSIX timestamps).

Changes:

• Make parameter cache timestamps timezone-aware (local timezone) and serialize parameter snapshot "ts" using ISO 8601 (with UTC offset).
• Change default dataset timestamp string formats (run_timestamp, completed_timestamp, raw_time_to_str_time) to include %z (UTC offset) and update parsing/export tests accordingly.
• Fix manual timezone offset formatting in the Tektronix AWG70000A driver and update other timestamp producers (logger, widget, drivers) to use tz-aware datetimes.

Reviewed changes

Copilot reviewed 20 out of 20 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
tests/parameter/test_snapshot.py	Update snapshot timestamp parsing to fromisoformat and use tz-aware now.
tests/parameter/test_parameter_cache.py	Use tz-aware datetimes in cache timestamp assertions.
tests/parameter/test_group_parameter.py	Use tz-aware datetimes in group parameter cache timestamp assertions.
tests/parameter/test_get_latest.py	Use tz-aware datetimes in get_latest timestamp assertions.
tests/dataset/test_links.py	Use tz-aware datetimes when generating synthetic timestamps.
tests/dataset/test_dataset_loading.py	Parse default-formatted timestamps with %z using datetime.strptime.
tests/dataset/test_dataset_export.py	Add coverage asserting exported timestamps include UTC offset and match raw instants.
src/qcodes/parameters/parameter_base.py	Serialize snapshot "ts" with datetime.isoformat(..., timespec="seconds").
src/qcodes/parameters/cache.py	Store cache timestamps as tz-aware local time; update expiration cutoff logic.
src/qcodes/logger/logger.py	Generate log file date string from tz-aware local time.
src/qcodes/interactive_widget.py	Compute elapsed time using UTC-aware fromtimestamp (DST-safe).
src/qcodes/instrument_drivers/tektronix/AWG70000A.py	Fix timezone offset generation using tz-aware local time (DST-correct).
src/qcodes/instrument_drivers/Keysight/Infiniium.py	Make screenshot filename timestamp tz-aware local time.
src/qcodes/dataset/sqlite/queries.py	Render raw POSIX timestamps via tz-aware local time; default format includes %z.
src/qcodes/dataset/sqlite/db_overview.py	Convert timestamps via fromtimestamp(..., tz=UTC).astimezone() before formatting.
src/qcodes/dataset/data_set_protocol.py	Update default dataset timestamp formats to include %z and clarify docs.
pyproject.toml	Stop ignoring DTZ rules now that code is updated.
docs/examples/DataSet/Linking to parent datasets.ipynb	Use tz-aware datetime.now(datetime.UTC) in the example.
docs/changes/newsfragments/8345.improved_driver	Document AWG70000A timezone-offset fix.
docs/changes/newsfragments/8345.breaking	Document breaking changes in timestamp formatting and cache timestamp tz-awareness.

Suppressed comments (1)

src/qcodes/parameters/cache.py:206

• oldest_accepted_timestamp is computed by subtracting a timedelta from a local-time (zoneinfo) datetime. Datetime arithmetic with local zoneinfo does not normalize offsets across DST transitions, so this can miscompute the cutoff instant around DST changes and lead to incorrect cache expiration decisions. Compute the cutoff in UTC and compare in UTC to make the age check timeline-correct.

        oldest_accepted_timestamp = datetime.now(UTC).astimezone() - timedelta(
            seconds=self._max_val_age
        )
        too_old = self._timestamp < oldest_accepted_timestamp
        return too_old