fix: BJData size calculation overflow

[thevilledev]

Adds pre-multiplication overflow detection to catch cases where dimension products would exceed size_t max. The previous check only detected when overflow resulted in exactly 0 or SIZE_MAX, missing other cases.

Retains the original post-multiplication check for backward compatibility. Adds tests verifying overflow detection with dimensions (2^32+1)×(2^32), which previously overflowed silently to 2^32.

This prevents custom SAX handlers from receiving incorrect array sizes that could lead to buffer overflows.

• The changes are described in detail, both the what and why.
• If applicable, an existing issue is referenced.
• The Code coverage remained at 100%. A test case for every new line of code.
• If applicable, the documentation is updated.
• The source code is amalgamated by running make amalgamate.

[nlohmann]

Please rebase to the latest develop branch to fix the GCC-related errors.

[coveralls]

coverage: 99.188%. remained the same
when pulling 02a59cf on thevilledev:fix/int-overflow-bjdata
into 6b91993 on nlohmann:develop.

[nlohmann]

Looks good to me.

[nlohmann]

Thanks!