chore(writer): enable native writer by default [backport 4.0]

[dd-octo-sts]

Backport c2e0ab9 from #15278 to 4.0.

Description

Enables the native writer by default. The native writer can still be disabled through _DD_TRACE_WRITER_NATIVE.

Testing

All tests are run with the native writer. The native writer have also been enabled on some services internally for dogfooding purposes.

Risks

This changes the logic behind trace export and client-side stats computation (for customers who enabled it). We expect no change in behavior for trace exporting. Client-side stats behavior may show some differences as the current python implementation is not fully compliant with the client-side stats spec.

[github-actions]

CODEOWNERS have been resolved as:

.gitlab/benchmarks/bp-runner.microbenchmarks.fail-on-breach.yml         @DataDog/python-guild @DataDog/apm-core-python
ddtrace/internal/settings/_config.py                                    @DataDog/python-guild @DataDog/apm-sdk-capabilities-python
tests/contrib/mcp/conftest.py                                           @DataDog/ml-observability
tests/integration/test_integration.py                                   @DataDog/apm-core-python
tests/telemetry/test_writer.py                                          @DataDog/apm-python

[github-actions]

Bootstrap import analysis

Comparison of import times between this PR and base.

Summary

The average import time from this PR is: 240 ± 2 ms.

The average import time from base is: 235 ± 2 ms.

The import time difference between this PR and base is: 5.52 ± 0.1 ms.

Import time breakdown

The following import paths have grown:

ddtrace.auto 7.613 ms (3.17%)

ddtrace 7.613 ms (3.17%)

ddtrace.trace 7.613 ms (3.17%)

The following import paths have shrunk:

ddtrace.auto 2.176 ms (0.91%)

ddtrace.bootstrap.sitecustomize 1.509 ms (0.63%)

ddtrace.bootstrap.preload 1.509 ms (0.63%)

ddtrace.internal.remoteconfig.client 0.674 ms (0.28%)

multiprocessing.sharedctypes 0.075 ms (0.03%)

ctypes 0.040 ms (0.02%)

multiprocessing 0.043 ms (0.02%)

multiprocessing.context 0.043 ms (0.02%)

multiprocessing.reduction 0.043 ms (0.02%)

pickle 0.043 ms (0.02%)

ddtrace 0.667 ms (0.28%)

ddtrace.internal._unpatched 0.028 ms (0.01%)

json 0.028 ms (0.01%)

json.decoder 0.028 ms (0.01%)

re 0.028 ms (0.01%)

enum 0.028 ms (0.01%)

types 0.028 ms (0.01%)

[emmettbutler]

force-merging because tests other than benchmarks are complete