Fixes #28865 (review)
# FUZZ=policy_estimator UBSAN_OPTIONS="suppressions=/root/fuzz_dir/scratch/fuzz_gen/code/test/sanitizer_suppressions/ubsan:print_stacktrace=1:halt_on_error=1:report_error_type=1" ./src/test/fuzz/fuzz /tmp/crash-154b42214e70781a9c1ad72d3f2693913dcf8c06
...
policy/fees.cpp:632:27: runtime error: implicit conversion from type 'unsigned int' of value 4294574080 (32-bit, unsigned) to type 'int' changed the value to -393216 (32-bit, signed)
[#0](/bitcoin-bitcoin/0/) 0x55cbbe10daee in CBlockPolicyEstimator::processBlockTx(unsigned int, CTxMemPoolEntry const*) src/policy/fees.cpp:632:27
[#1](/bitcoin-bitcoin/1/) 0x55cbbe10e361 in CBlockPolicyEstimator::processBlock(unsigned int, std::vector<CTxMemPoolEntry const*, std::allocator<CTxMemPoolEntry const*>>&) src/policy/fees.cpp:680:13
[#2](/bitcoin-bitcoin/2/) 0x55cbbd84af48 in policy_estimator_fuzz_target(Span<unsigned char const>)::$_1::operator()() const src/test/fuzz/policy_estimator.cpp:69:40
[#3](/bitcoin-bitcoin/3/) 0x55cbbd84af48 in unsigned long CallOneOf<policy_estimator_fuzz_target(Span<unsigned char const>)::$_0, policy_estimator_fuzz_target(Span<unsigned char const>)::$_1, policy_estimator_fuzz_target(Span<unsigned char const>)::$_2, policy_estimator_fuzz_target(Span<unsigned char const>)::$_3>(FuzzedDataProvider&, policy_estimator_fuzz_target(Span<unsigned char const>)::$_0, policy_estimator_fuzz_target(Span<unsigned char const>)::$_1, policy_estimator_fuzz_target(Span<unsigned char const>)::$_2, policy_estimator_fuzz_target(Span<unsigned char const>)::$_3) src/./test/fuzz/util.h:43:27
[#4](/bitcoin-bitcoin/4/) 0x55cbbd84af48 in policy_estimator_fuzz_target(Span<unsigned char const>) src/test/fuzz/policy_estimator.cpp:38:9
[#5](/bitcoin-bitcoin/5/) 0x55cbbda1cc18 in std::function<void (Span<unsigned char const>)>::operator()(Span<unsigned char const>) const /usr/bin/../lib/gcc/x86_64-linux-gnu/13/../../../../include/c++/13/bits/std_function.h:591:9
[#6](/bitcoin-bitcoin/6/) 0x55cbbda1cc18 in LLVMFuzzerTestOneInput src/test/fuzz/fuzz.cpp:178:5
[#7](/bitcoin-bitcoin/7/) 0x55cbbd26a944 in fuzzer::Fuzzer::ExecuteCallback(unsigned char const*, unsigned long) (/root/fuzz_dir/scratch/fuzz_gen/code/src/test/fuzz/fuzz+0x190e944) (BuildId: ffb89e0b86c093ca3bdeae6f85537737a4e3b42d)
[#8](/bitcoin-bitcoin/8/) 0x55cbbd253916 in fuzzer::RunOneTest(fuzzer::Fuzzer*, char const*, unsigned long) (/root/fuzz_dir/scratch/fuzz_gen/code/src/test/fuzz/fuzz+0x18f7916) (BuildId: ffb89e0b86c093ca3bdeae6f85537737a4e3b42d)
[#9](/bitcoin-bitcoin/9/) 0x55cbbd25945a in fuzzer::FuzzerDriver(int*, char***, int (*)(unsigned char const*, unsigned long)) (/root/fuzz_dir/scratch/fuzz_gen/code/src/test/fuzz/fuzz+0x18fd45a) (BuildId: ffb89e0b86c093ca3bdeae6f85537737a4e3b42d)
[#10](/bitcoin-bitcoin/10/) 0x55cbbd284026 in main (/root/fuzz_dir/scratch/fuzz_gen/code/src/test/fuzz/fuzz+0x1928026) (BuildId: ffb89e0b86c093ca3bdeae6f85537737a4e3b42d)
[#11](/bitcoin-bitcoin/11/) 0x7fe4aa8280cf (/lib/x86_64-linux-gnu/libc.so.6+0x280cf) (BuildId: 96ab1a8f3b2c9a2ed37c7388615e6a726d037e89)
[#12](/bitcoin-bitcoin/12/) 0x7fe4aa828188 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x28188) (BuildId: 96ab1a8f3b2c9a2ed37c7388615e6a726d037e89)
[#13](/bitcoin-bitcoin/13/) 0x55cbbd24e494 in _start (/root/fuzz_dir/scratch/fuzz_gen/code/src/test/fuzz/fuzz+0x18f2494) (BuildId: ffb89e0b86c093ca3bdeae6f85537737a4e3b42d)
SUMMARY: UndefinedBehaviorSanitizer: implicit-integer-sign-change policy/fees.cpp:632:27 in
# base64 /tmp/crash-154b42214e70781a9c1ad72d3f2693913dcf8c06
AQEAAAAAADkFlVwAAQEAAAAAADkFlZVcACTDSSsP3746IAZrH48khwMAAQEB/QEALQAACwAAAAAA
FgAAAAAAAQAABgAAAAAAAAAAAAAAAAAAACcQAAAAAAAAAAAAAAAAAAAAAAD6AAAAOQWVXAABAQAA
AAAAOQWVlVwAIMNJKw/fvjogBmsfjySHAwABAQH9AQAtAAALAAAAAAAAAAABAAAGAAAAAAAAAAAA
AAAAAAAAJxAAAAAAAAAAAAAAAAAAAAAAAPr/AAAAAAAAAAAAAAQAAAAA/wAAAAAAAAAAAAAEAAAA
AAEBAeAIAVwBXAAA/jbSBvwBKABSKBwBYgEB2wAEkvXInHYAAAAAAAAAvgAAAAAA/9//6v8e/xIk
MgAlAiUAOw==