Drop support for Python 3.8

Drop Python 3.8 support in 5 Pulsar-compatible packages
(job_metrics, tool_util, tool_util_models, util, objectstore)
and run pyupgrade --py310-plus on their source code.

- Bump requires-python from >=3.8 to >=3.10 in all 5 packages
- Remove Python 3.8 and 3.9 classifiers
- Remove ruff per-file-ignores for UP rules on these paths
- Remove backports.zoneinfo conditional dependency
- Remove pydyf<0.11 pin from conditional-requirements.txt
- Update Makefile pyupgrade target (remove PY38_PYUPGRADE_PATHS)
- Update CI workflow to test with Python 3.10 instead of 3.8

Clean up unused deprecated typing imports after pyupgrade

Remove now-unused typing imports (Dict, List, Optional, Set, Tuple,
Type, Union) that became dead after pyupgrade --py310-plus converted
annotations to use built-in types and | syntax.

Also run ruff check --fix --select=UP007,UP045 across the entire
codebase to convert remaining Optional[X] -> X | None and
Union[X, Y] -> X | Y patterns.

Enable ruff UP007/UP045 for Python 3.10 union syntax

Remove UP007 (Union[X,Y] -> X | Y) and UP045 (Optional[X] -> X | None)
from the ruff ignore list and convert all type aliases across the
codebase. These rules were deferred while Python 3.9 was supported;
requires-python is now >=3.10.

A custom script was used because neither ruff --fix nor
pyupgrade --py310-plus converts Optional[X]/Union[X,Y] in type alias
positions (e.g. X = Union[A, B]) — they only handle annotation
positions (e.g. def f(x: Optional[int])). All 167 violations were
module-level type aliases. A few edge cases were fixed manually:
single-element Union[X,], typing.Union qualified refs, runtime
Optional[type] calls, and Annotated[Optional[...]] pydantic fields.

Fix UP007 autofix regression with string forward reference type aliases

Commit fa6bd955a0 enabled ruff UP007/UP045 and auto-fixed
module-level type aliases using Union with string forward
references, producing invalid 'str | str' expressions.

This was a known ruff bug (charliermarsh/ruff#826) that has since
been fixed in later ruff versions, but this codebase was
converted before the fix was in place.

Revert to Union syntax and restore TYPE_CHECKING imports that
ruff's TCH rule cleaned up as a side effect when it thought the
forward references were unused.

scripts/check_python.py

@@ -3,8 +3,6 @@ If the current installed Python version is not supported, prints an error
 message to stderr and returns 1
 """
 
-from __future__ import print_function
-
 import sys
 
 MIN_VERSION_TUPLE = (3, 10)
@@ -17,15 +15,12 @@ def check_python():
     else:
         version_string = ".".join(str(_) for _ in sys.version_info[:3])
         min_version_string = ".".join(str(_) for _ in MIN_VERSION_TUPLE)
-        msg = """ERROR: Your Python version is: {}
-Galaxy is currently supported on Python >={} .
+        msg = f"""ERROR: Your Python version is: {version_string}
+Galaxy is currently supported on Python >={min_version_string} .
 To run Galaxy, please install a supported Python version.
 If a supported version is already installed but is not your default,
 https://docs.galaxyproject.org/en/latest/admin/python.html contains instructions
-on how to force Galaxy to use a different version.""".format(
-            version_string,
-            min_version_string,
-        )
+on how to force Galaxy to use a different version."""
         print(msg, file=sys.stderr)
         raise Exception(msg)