Suppress GCC false positive -Wstringop-overflow in enqueue_bulk (#456)

[AnmolS05]

Fixes #456.

Problem

GCC 14, 15, and 16 emit a spurious -Wstringop-overflow diagnostic warning under -O2 and -O3 when enqueue_bulk is called with an explicit producer token and an iterator materializing move-only elements upon dereference. Because -Wstringop-overflow is enabled by default under -O2, -Werror builds fail outright.

The warning originates from this->tailIndex.load() inside ExplicitProducer::enqueue_bulk, reached via inner_enqueue_bulk. GCC's value range analysis considers an inlined path where token.producer is null, concluding that the atomic load operates on address zero.

Solution

As discussed and approved in #456, this PR adds a localized diagnostic pragma around the static_cast<ExplicitProducer*>(token.producer)->... call in inner_enqueue_bulk, guarded by #if defined(__GNUC__) && !defined(__clang__) && __GNUC__ >= 7.

• No codegen change: Purely diagnostic suppression with zero runtime overhead.
• Compiler compatibility: Guarded by __GNUC__ >= 7 to avoid -Wpragmas warnings on older GCC versions (GCC 4.8 – 6) where -Wstringop-overflow does not exist.
• Safety: Avoids optimizer assumptions like __builtin_unreachable().

Testing

• Reproduced and verified fix on MinGW GCC 15.2.0 with -O2 -std=c++17 -Wall -Wextra -Werror (diagnostic completely silenced).
• Added unit test enqueue_bulk_producer_token_generating_iterator in tests/unittests/unittests.cpp.
• Executed unit test suite (8 iterations): 46 / 46 unit tests passed.
• Executed fuzz test suite under -O2: all randomized tests passed.

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