Drop template-id from ctor/dtor names in numeric/ (GCC 14/15 -Werror=template-id-cdtor)

[lyskov-ai]

Summary

GCC 14+ enforces -Werror=template-id-cdtor: a class template may not name its own constructors or destructors with explicit template arguments — the injected-class-name must be used without <...>. numeric/MathVector.hh, numeric/MathMatrix.hh, and numeric/histograms/OneDHistogram.hh declared constructors (and, for the first two, the destructor) in the disallowed form, e.g.:

MathVector< T>() : ...
explicit MathVector< T>( const Size SIZE, ... ) : ...
~MathVector< T>() { ... }
OneDHistogram<key1>()= default;

Under GCC 14/15 in C++20 mode this fails to compile (error: template-id not allowed for constructor/destructor in C++20). The numeric/ occurrences broke the plain library debug build before it could even reach basic/ or core/. The OneDHistogram.hh occurrence is more subtle: its default constructor is only instantiated by a unit test (numeric/histograms/OneDHistogram.cxxtest.hh), not by any library code, so it slipped past a library-only build and only surfaced when building/running the unit test suite — this is what broke CI on the previous version of this PR.

This drops the < T> / <key1> from the constructor and destructor declarator-ids, making them consistent with the copy constructors in the same classes, which already use the correct injected-class-name form. Return types, operators, and new expressions that legitimately use the templated name are untouched. Pure syntactic correction, no semantic change.

Verified with a clean mode=debug library build and mode=debug cat=test unit-test build under GCC 15 (this machine's default), plus a full library build under GCC 14 — both fully green. A targeted scan of source/src, source/test, and source/src/devel for the same declaration pattern turned up no other occurrences.

Relationship to existing GCC 15 PRs (#555, #556)

This is not the first attempt at the GCC 15 build. Two earlier community PRs are still open and overlap with this one:

• Fix C++20 template-id errors in constructors/destructors #555 — "Fix C++20 template-id errors in constructors/destructors" (@saberger). This contains the identical MathVector/MathMatrix/OneDHistogram template-id fix as this PR, and additionally covers core/scoring/lkball/LK_DomeEnergy.cc, protocols/forge/remodel/RemodelGlobalFrame.cc, utility/options/VectorOption_T_.hh, two unit tests, and tools/build/basic.settings — none of which have this same template-id-cdtor pattern currently (checked directly), so those are addressing separate GCC 15 issues.
• Fixes for compiling with gcc15 #556 — "Fixes for compiling with gcc15" (@roccomoretti). The broader assorted GCC 15 fixes. Does not touch these three files.

Because #555 already lands the same fix, #723 is largely redundant with the numeric/ slice of that effort. It's offered as a minimal, narrowly-scoped version of just the template-id-cdtor correction in case it's useful to merge the build-blocking part independently; otherwise #555 (combined with #556, per its author's note) supersedes it. Closing this in favor of #555 + #556 is fine if the maintainers prefer to consolidate the GCC 15 work.

Note on diff size

This is a small change (three files, ~18 lines) — below the usual bundling threshold — but it is the complete fix for this pattern across the codebase: a scan of source/src, source/test, and source/src/devel found no other occurrences of a class template naming its own constructor/destructor with a template-id. Kept narrowly scoped to this one toolchain-compatibility pattern.

[roccomoretti]

Looks like this needs beautification: https://b3.graylab.jhu.edu/test/915440