deps: pin black==26.5.1 and mypy==2.3.0 to match TSC

[jacalata]

Motivation

The two Tableau-owned Python packages were on divergent dev-tool versions:

	tabcmd (before)	tabcmd (after)	TSC
black	>=22,<23	==26.5.1	==26.5.1
mypy	unpinned	==2.3.0	==2.3.0

Anyone working on both repos has to keep swapping black versions in
their local env. Match TSC's pins on the tabcmd side; the older repo is
the outlier.

Behavior change

For contributors:

• black 26 reformats 9 files (whitespace around decorators, blank
  lines after imports). No behavior change; all diffs are whitespace or
  trailing-comma noise.
• [tool.black] target-version bumped from py310-py311 to
  py310-py314, matching requires-python = ">=3.10" and the
  classifiers list.
• Dropped required-version = 22 line from [tool.black]; the version
  pin in [test] is sufficient.

mypy 2.3 caught one pre-existing issue in tabcmd/version.py:
from tabcmd._version import version reimported the same name inside a
fallback branch, shadowing the version: str = "unknown" annotation.
Renamed the fallback import to _pyinstaller_version. Same string ends
up in version.

Test plan

• black . --check passes under black 26.5.1
• mypy tabcmd tests passes with 0 errors under mypy 2.3.0
• Full unit-test suite: 337 passed, 2 skipped

🤖 Generated with Claude Code

[github-actions]

Coverage Report

File	Stmts	Miss	Cover	Missing
tabcmd
__main__.py	12	12	12	0%
_version.py	11	11	11	0%
tabcmd.py	15	15	15	0%
version.py	10	6	6	40%
tabcmd/commands
commands.py	10	10	10	0%
constants.py	77	18	18	77%
server.py	135	18	18	87%
tabcmd/commands/auth
session.py	394	50	50	87%
tabcmd/commands/datasources_and_workbooks
datasources_and_workbooks_command.py	157	18	18	89%
datasources_workbooks_views_url_parser.py	142	5	5	96%
delete_command.py	60	16	16	73%
export_command.py	120	25	25	79%
get_url_command.py	127	47	47	63%
publish_command.py	123	28	28	77%
runschedule_command.py	21	7	7	67%
tabcmd/commands/extracts
create_extracts_command.py	42	8	8	81%
decrypt_extracts_command.py	27	2	2	93%
delete_extracts_command.py	37	6	6	84%
encrypt_extracts_command.py	27	2	2	93%
extracts.py	20	2	2	90%
reencrypt_extracts_command.py	27	2	2	93%
refresh_extracts_command.py	48	10	10	79%
tabcmd/commands/group
create_group_command.py	29	5	5	83%
delete_group_command.py	27	2	2	93%
tabcmd/commands/project
create_project_command.py	46	8	8	83%
delete_project_command.py	35	4	4	89%
publish_samples_command.py	30	4	4	87%
tabcmd/commands/site
create_site_command.py	34	5	5	85%
delete_site_command.py	27	2	2	93%
edit_site_command.py	38	2	2	95%
list_command.py	77	12	12	84%
list_sites_command.py	29	2	2	93%
tabcmd/commands/user
add_users_command.py	29	5	5	83%
create_site_users.py	58	11	11	81%
create_users_command.py	59	9	9	85%
delete_site_users_command.py	43	5	5	88%
user_data.py	222	31	31	86%
tabcmd/execution
_version.py	2	2	2	0%
global_options.py	125	8	8	94%
localize.py	66	11	11	83%
logger_config.py	60	6	6	90%
tabcmd_controller.py	42	7	7	83%
TOTAL	2874	459	84%