Fix tutor2pp segfault from double-free in createObjects

[mchamberland]

Summary

• Fix a segmentation fault in tutor2pp (and any user code derived from EGS_SimpleApplication) caused by a double-free in EGS_ObjectFactory::createObjects().
• createObjects() now deletes its working EGS_Input pointer only when it extracted the section itself via takeInputItem(), matching the ownership pattern already used in EGS_BaseGeometry::createGeometry().

Fixes #1140

Root cause

EGS_SimpleApplication takes the source definition block from the input file, passes that pointer to EGS_BaseSource::createSource(), and then deletes it. Inside createSource() → createObjects(), when the argument is already a source definition section, the local input pointer aliases the caller's pointer. An unconditional delete input at the end of createObjects() (added in def34e2 to fix a sanitizer-reported leak) freed memory that EGS_SimpleApplication then deleted again.

Advanced applications (EGS_AdvancedApplication, egs_brachy, tutor7pp, etc.) were unaffected because they pass the full input file; createObjects() takes the section internally and owns that extracted pointer.

Reasoning / alignment with #1140

Ernesto Mainegra identified the same cause on #1140 and suggested two approaches:

1. Pass a copy into createObjects so the factory frees its copy while the caller keeps the original.
2. Adjust deletion in egs_simple_application.cpp (Matt Inglis Whalen's workaround was to remove delete source_input entirely).

This PR follows option 1 in intent—make ownership explicit at the factory—without copying EGS_Input. When the caller passes an already-extracted section, createObjects() leaves it for the caller to delete; when it extracts the section from a larger input (the advanced-application path), it deletes what it took. That preserves the 2021 leak fix for the advanced path while fixing the SimpleApplication double-free, and avoids the leak that would result from simply removing delete source_input in egs_simple_application.cpp.

Test plan

• Rebuild libegspp and run tutor2pp -i test1.egsinp -p tutor_data on macOS (eb-dev config): completes with deposited/transmitted energy fractions.
• CI / upstream reviewer: confirm tutor2pp and an EGS_AdvancedApplication example still run on Linux.

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