These warnings are about conversion from `size_t` to a smaller type[1],
and in this case because `gdIOCtx` works with `int` lengths. Two of
these warnings are harmless, and we resolve them by using `size_t` in
the first place, and adding a cast (plus an assertion), respectively.
The others actually hint at potential issues when reading image data
with more than `INT_MAX` bytes; we catch that upfront, and throw a
`ValueError` and a warning, respectively.
[1] <https://learn.microsoft.com/en-us/cpp/error-messages/compiler-warnings/compiler-warning-level-3-c4267>
c1f7b87fb1