Add --output json to flow ls, work-pool ls, task-run ls, concurrency-limit ls

[h1whelan]

Summary

Related to #19483

Adds --output json / -o json support to four CLI list commands that were missing it:

• flow ls
• work-pool ls
• task-run ls
• concurrency-limit ls

Each follows the established pattern from flow-run ls and deployment ls:

• Add --output / -o option (accepts "json")
• When output == "json", serialize response objects with orjson.dumps(..., option=orjson.OPT_INDENT_2) and print
• When not set, render the existing Rich table as before
• Empty results return [] in JSON mode instead of a text message
• Invalid format values produce a clear error message

Also adds proper empty-list handling (exit_with_success) for flow ls and task-run ls where it was previously missing.

Changes

File	Change
src/prefect/cli/flow.py	Add --output json to flow ls
src/prefect/cli/work_pool.py	Add --output json to work-pool ls
src/prefect/cli/task_run.py	Add --output json to task-run ls
src/prefect/cli/concurrency_limit.py	Add --output json to concurrency-limit ls
tests/cli/test_flow.py	Tests for flow ls JSON output
tests/cli/test_task_run.py	Tests for task-run ls JSON output
tests/cli/test_work_pool.py	Tests for work-pool ls JSON output
tests/cli/test_concurrency_limit.py	New test file for concurrency-limit ls JSON output

Test plan

• JSON output returns valid JSON array for each command
• Empty results return [] (not a text message) in JSON mode
• Invalid format (e.g. -o xml) returns error with exit code 1
• State/name filters work with JSON output (task-run ls --state Running -o json)
• Existing table output is unchanged when --output is not specified

[codspeed-hq]

Merging this PR will not alter performance

✅ 2 untouched benchmarks

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_{Comparing h1whelan:add-output-json-to-cli-ls-commands (b5b1082) with main (13e96b7)}