fix: disable remote configuration by default in Lambda

Remote configuration relies on /dev/shm for shared memory, which is
unavailable in AWS Lambda. Set DD_REMOTE_CONFIGURATION_ENABLED=false
before ddtrace loads (following the same pattern used for
DD_TRACE_STATS_COMPUTATION_ENABLED and
DD_INSTRUMENTATION_TELEMETRY_ENABLED) so the tracer knows RC is
disabled from the start.

This is a defense-in-depth companion to the primary fix in dd-trace-py
(DataDog/dd-trace-py#17550) which skips the shared memory allocation
entirely when in_aws_lambda() is detected.

Integration test snapshots will need regenerating since ddtrace startup
behavior changes slightly when RC is disabled from the start vs
disabled later by the ASM Lambda guard.

Resolves: #785

Author: zarirhamza

datadog_lambda/config.py

@@ -141,6 +141,11 @@ def _reset(self):
         "enabled" if config.fips_mode_enabled else "not enabled",
     )
 
+# Remote configuration relies on /dev/shm which is unavailable in Lambda.
+# Disable it before ddtrace loads to avoid the shared-memory warning.
+if "DD_REMOTE_CONFIGURATION_ENABLED" not in os.environ:
+    os.environ["DD_REMOTE_CONFIGURATION_ENABLED"] = "false"
+
 # disable css to prevent double counting in lambda
 os.environ["DD_TRACE_STATS_COMPUTATION_ENABLED"] = "false"