Fix compilation on GCC 15 by including <cstdint>

[skooch]

As per the GCC 15 porting guide, section "Header dependency changes": https://gcc.gnu.org/gcc-15/porting_to.html#header-dep-changes

Some C++ Standard Library headers have been changed to no longer include other headers that were being used internally by the library. As such, C++ programs that used standard library components without including the right headers will no longer compile.

In particular, the following headers are used less widely within libstdc++ and may need to be included explicitly when compiling with GCC 15:

<stdint.h> (for int8_t, int32_t etc.) and <cstdint> (for std::int8_t, std::int32_t etc.)
<ostream> (for std::endl, std::flush etc.)

<cstdint> must now be explicitly included to use these types and was missing from CharData.h.

This resolves issue #2545

Thanks for contributing!

• Have you updated CHANGELOG.md?

[chearon]

Thanks

[skooch]

@chearon No rush, but when would we expect a release to be cut after merging this? Just want to know when I should check back, since I have compiler flags littered in builds at work.

[chearon]

I plan to be working on node-canvas next week, and I can do a patch release then. No release is quick to do until we get our prebuilds overhauled 😕

[chearon]

@skooch I did indeed run into a problem, but as of now 3.2.1 is released

[skooch]

@chearon Thank you!