TASK-185818 fix race condition during new object createion

[balupillai]

Note

Medium Risk
Touches core GC object-allocation ordering and locking, so mistakes could cause hard-to-debug memory corruption or deadlocks; logging-only changes in modules are low risk.

Overview
Fixes a potential GC race in src/lgc.c during new_obj allocation by blocking the collector while linking the new object into the heap and only then calling make_grey, preventing the GC from seeing a grey-stack entry for an object not yet fully linked.

Standardizes buffer-overflow warnings in modules/curl.c and modules/pcre.c by replacing direct fprintf(stderr, ...) calls with thrlua_log(..., DCRITICAL, ...) so these events go through the shared logging mechanism.

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