Robust handling of root-finding errors in fitpt.m0: skip genes with uniroot failures and return NA instead of stopping analysis

[Ye1203]

When using fitpt.m0, some genes may cause an error in the uniroot call:

Error in uniroot(function(eta)): f() values at end points not of opposite sign,

because the interval endpoints have the same sign

(i.e., both digamma(1e-10 * meanN) - log(1e-10) + meanA and digamma(1e+10 * meanN) - log(1e+10) + meanA are positive or both negative).

In the original code, such errors would stop the entire lamian_test workflow, resulting in no output even for unaffected (normal) genes, and sometimes secondary errors like $ operator is invalid for atomic vectors.

In this patch, I modify fitpt.m0 to skip those problematic genes by returning NA when root-finding fails, and propagate this behavior so that corresponding entries are NA in the output from lamian_test. This ensures that analyses continue even if some genes cannot be fit, and all valid results for normal genes are still returned.

This change increases the robustness and fault-tolerance of the package, ensuring stable analysis even with problematic or edge-case data.