formula: onqtam/doctest

[MeteorsLiu]

Adds the onqtam/doctest LLAR Formula from the verified 2.3.3 tag through current upstream tags, preserving the header, license, CMake helper outputs, and relocatable include metadata. The Conan consumer passes on explicit darwin/arm64, including a cache-hit rerun.

Closes #318

[fennoai]

The packaging layout and pkg-config metadata are consistent with the reference recipe, and the requested v2.4.11 consumer passes on Linux. However, the declared lower bound is not usable on the repository’s current Linux validation environment; please raise the threshold to the first compatible upstream tag (or otherwise preserve compatibility) before merging.

Verification: llar test --verbose ./onqtam/doctest@2.3.3 --os linux --arch amd64 fails in the consumer compile, while 2.4.6 and v2.4.11 pass.

[fennoai]

[P1] Do not claim compatibility from 2.3.3

This floor makes the formula select this implementation for 2.3.3 through the later tags, but the exact 2.3.3 consumer cannot compile on current Linux/glibc: doctest declares altStackMem[4 * SIGSTKSZ], and SIGSTKSZ is not an integral constant expression there. llar test --verbose ./onqtam/doctest@2.3.3 --os linux --arch amd64 reproduces the failure at the consumer compile, whereas 2.4.6 and v2.4.11 pass. Raise fromVer to the first compatible tag (2.4.6 in this environment), or add a separate compatible implementation/patch so selecting the advertised lower versions does not produce an unusable package.