Add codspeed benchmarks

[hynek]

If we want to judge PRs like #821 we need some kind of objective baseline.

[codspeed-hq]

Congrats! CodSpeed is installed 🎉

🆕 10 new benchmarks were detected.

You will start to see performance impacts in the reports once the benchmarks are run from your default branch.

Detected benchmarks

• test_bind: 17.5 ms
• test_bind_and_clear_contextvars: 66.2 ms
• test_create_bound_logger: 82.2 ms
• test_log_event_console: 345.8 ms
• test_log_event_filtered_out: 1.7 ms
• test_log_event_json: 151.7 ms
• test_log_event_key_value: 126.2 ms
• test_log_event_with_contextvars: 131.4 ms
• test_log_exception_as_dict: 910 ms
• test_log_exception_formatted: 3.4 s

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