chore(profiling): more Profiler Stats

[KowalskiThomas]

Description

https://datadoghq.atlassian.net/browse/PROF-13820

This PR adds new information in the Internal Metadata payload of profiles:

• Whether the memcpy-based copy_memory implementation is enabed
• The number of errors that it encountered.

This is meant to be used to check that there aren't any typically problematic cases in real-life workloads.

[cit-pr-commenter-54b7da]

Codeowners resolved as

ddtrace/internal/datadog/profiling/dd_wrapper/include/profiler_stats.hpp  @DataDog/profiling-python
ddtrace/internal/datadog/profiling/dd_wrapper/src/profiler_stats.cpp    @DataDog/profiling-python
ddtrace/internal/datadog/profiling/stack/echion/echion/vm.h             @DataDog/profiling-python
ddtrace/internal/datadog/profiling/stack/src/echion/vm.cc               @DataDog/profiling-python
ddtrace/internal/datadog/profiling/stack/src/sampler.cpp                @DataDog/profiling-python
tests/profiling/collector/test_copy_memory_stats.py                     @DataDog/profiling-python

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Report fast-copy status from active backend

fast_copy_enabled is derived from use_alternative_copy_memory() (the env var), but init_safe_copy() can still fall back to non-memcpy readers when init_segv_catcher() fails; in that scenario this field is emitted as true even though memcpy-based copying is not actually active. That makes the new metadata unreliable for diagnosing production behavior.

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