feat: add --output json support to task-run ls command

[cluster2600]

Summary

Adds machine-readable JSON output to the prefect task-run ls command, following the existing pattern established in task-run inspect, flow-run ls, and deployment ls.

Changes

• Added --output/-o option to task-run ls accepting "json" format
• When --output json is set, task runs are serialized via orjson with pretty-printing and printed to stdout
• Empty result returns a JSON empty array [] instead of the human-readable "No task runs found." message
• Existing Rich table rendering is preserved when the flag is not provided
• Added tests for: JSON output with task runs present, empty list case, and invalid format error

Usage

# Machine-readable JSON output
prefect task-run ls --output json
prefect task-run ls -o json

# Pipe-friendly usage
prefect task-run ls -o json | jq '.[].name'

Related

Related to #19483 (checks off task-run ls from the list)

Checklist

• Code follows the existing pattern (task_run.py inspect, flow_run.py, deployment.py)
• Tests added for both output modes
• No breaking changes to existing table output

[codspeed-hq]

Merging this PR will not alter performance

✅ 2 untouched benchmarks

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_{Comparing cluster2600:feat/task-run-ls-json-output (7c32a6b) with main (6712b8e)}