perf(native): load libcurl lazily in crash daemon

[jpnurmi]

Default the Native Unix crash daemon to runtime libcurl loading when SENTRY_LINK_CURL is not explicitly set. Keep explicit SENTRY_LINK_CURL=ON/OFF respected for the daemon. This lets sentry-crash avoid a direct libcurl dependency by default while the SDK continues to link libcurl directly unless configured otherwise.

Signal readiness to the parent process before starting the daemon transport. This keeps libcurl loading and curl transport initialization out of the startup handshake, while still starting the transport before the daemon enters its crash wait loop.

Important

Native/Unix daemon readiness now means the daemon IPC is ready, not that the HTTP transport has already been started. The daemon signals readiness to the parent first, then starts the transport immediately afterward. In practice, this keeps app startup from waiting on libcurl loading/initialization while preserving normal daemon-side sending once startup continues.

This shaves off ~50% startup time on Linux.

Before:

tests/benchmark.py::test_benchmark_init[native] PASSED
Min 9.189ms, Max 13.951ms, Mean 11.242ms, StdDev 1.806ms, Median 11.061ms, CPU 5.082ms
tests/benchmark.py::test_benchmark_backend[native] PASSED
Min 11.187ms, Max 13.468ms, Mean 12.581ms, StdDev 0.952ms, Median 12.821ms, CPU 5.773ms

After:

tests/benchmark.py::test_benchmark_init[native] PASSED
Min 4.384ms, Max 6.821ms, Mean 5.262ms, StdDev 1.083ms, Median 4.732ms, CPU 3.821ms
tests/benchmark.py::test_benchmark_backend[native] PASSED
Min 4.067ms, Max 5.052ms, Mean 4.438ms, StdDev 0.386ms, Median 4.341ms, CPU 3.282ms

See:

• Native: optimize backend startup on Linux #1852

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.85%. Comparing base (91ab69f) to head (8fc3b36).
⚠️ Report is 1 commits behind head on jpnurmi/feat/curl-link-option.

Additional details and impacted files

@@                        Coverage Diff                        @@
##           jpnurmi/feat/curl-link-option    #1955      +/-   ##
=================================================================
+ Coverage                          67.94%   75.85%   +7.91%     
=================================================================
  Files                                 91       94       +3     
  Lines                              21607    22246     +639     
  Branches                            3843     3962     +119     
=================================================================
+ Hits                               14681    16875    +2194     
+ Misses                              4952     4463     -489     
+ Partials                            1974      908    -1066     

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