Feature: Add overloads for SpecialFunctions with integer arguments

[bdrhill]

Problem

Several SpecialFunctions that take an integer as the first argument are missing overloads in the SpecialFunctions extension.

The extension comment notes: # TODO: add functions with integer arguments.

Affected functions

using SparseConnectivityTracer, SpecialFunctions

detector = TracerSparsityDetector()

# polygamma(m, x) - takes integer order m
jacobian_sparsity(x -> polygamma.(1, x), [2.0, 3.0], detector)
# MethodError: no method matching _polygamma(::Int64, ::GradientTracer...)

# zeta(s) 
jacobian_sparsity(x -> zeta.(x), [2.0, 3.0], detector)
# MethodError

# gamma_inc(a, x) - incomplete gamma
jacobian_sparsity(x -> [gamma_inc(x[1], x[2])[1]], [2.0, 0.5], detector)
# MethodError

# logabsgamma(x) - returns tuple (logabs, sign)
jacobian_sparsity(x -> [logabsgamma(x[1])[1]], [2.0], detector)
# MethodError

Implementation notes

For functions like polygamma(m::Int, x), the overload needs to handle the integer first argument as a constant (not a tracer), similar to how besseli(0, x) works.

For functions returning tuples like gamma_inc and logabsgamma, the tuple handling from #310 may need to be addressed first, or special handling added.