16 compilation error using clang on mac

[mmodat]

Fix Clang/C++17 compilation on macOS, plus static-analysis fixes and warning cleanup.
I ended up running cppcheck :)

@mjorgecardoso some these changes change output, please have a glance

Compilation fixes

• Remove the register storage-class specifier throughout seg-lib/seg-apps (rejected by recent Clang on macOS).
• Replace deprecated sprintf with bounded snprintf (22 call sites).
• Modernize CMake bootstrap: cmake_minimum_required(VERSION 3.10) before PROJECT(), drop conflicting 2.8/3.0.2 declarations, set CMP0135 when available.

Bug fixes found by static analysis (cppcheck 2.13, g++ -Wall -Wextra)

• seg_PatchMatch: k-NN result sorting compared PatchMatchResult* pointers (i.e. heap addresses) instead of dereferencing to the overloaded ANN-distance comparisons, so KNN results were effectively unsorted (_seg_PatchMatch.cpp::sortResults). 😱
• seg_PatchMatch: the same sort used vector::reserve() as if it were resize(), writing into size-0 vectors (undefined behavior).
• PatchMatchResult: copy constructor/assignment corrupted the copied values by routing them through buffer(), which pulled from never-copied fields; they now copy all members directly.
• seg_LoAd: an always-false condition (x > p && x < p) disabled second-best-class tracking in the partial-volume fractional-content step; corrected to compare against the best-class probability.
• seg_EM: the "Initial Loglik" verbose message was unreachable due to a redundant iter>0 guard.

Hardening

• Initialize all remaining uninitialized members in seg_PatchMatch, seg_fill_lesions, seg_fill_lesions_other, seg_EM constructors and copy operations; value-initialize the Priors_temp pointer array in seg_EM.
• Delete copy construction/assignment on seg_EM and seg_LabFusion (they own raw allocations; shallow copies would double-free).
• Pass std::string/std::vector<std::string> parameters by const reference.
• Remove unused parameters/variables; misc cleanups (self-assignment no-op, postfix→prefix iterator increment, vestigial always-true output-extension checks).

[mmodat]

Forgot to mention, the downloading of Eigen is also broken as it pulled from cmicdev at the time. I left it has it is and pointed cmake to the version in niftyreg/third-party.

[mmodat]

@mjorgecardoso Up!