Run clang-include-cleaner on all files in base/numerics

This change was generated by adding IWYU annotations and running:
clang-include-cleaner --insert --remove --edit base/numerics/*.[ch]*

Running clang-include-cleaner with the flag --html=<filename>
produces an HTML diagnostic page explaining why each headers are
needed. This showed some unused headers that were not automatically
removed by the tool (e.g. stddef.h, cstdlib and cassert). These were
removed manually.

Bug: 40248422
Change-Id: Idfefbdc4633b8849dbaf8a2c38df8ccbdf5346b9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5472985
Reviewed-by: danakj <[email protected]>
Commit-Queue: Jean-Philippe Gravel <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1291503}
diff --git a/base/numerics/safe_conversions_impl.h b/base/numerics/safe_conversions_impl.h
index c5c4726c..d322fafd 100644
--- a/base/numerics/safe_conversions_impl.h
+++ b/base/numerics/safe_conversions_impl.h
@@ -5,6 +5,9 @@
 #ifndef BASE_NUMERICS_SAFE_CONVERSIONS_IMPL_H_
 #define BASE_NUMERICS_SAFE_CONVERSIONS_IMPL_H_
 
+// IWYU pragma: private, include "base/numerics/safe_conversions.h"
+
+#include <stddef.h>
 #include <stdint.h>
 
 #include <concepts>