DPL: move topological sort in a separate file

[ktf]

Simplifies testing.

[github-actions]

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[ktf]

@ehellbar this is a minimal reproducer, apparently (after moving a bunch of stuff out of line).

[alibuild]

Error while checking build/O2/fullCI_slc9 for accb5c1 at 2025-07-09 08:57:

## sw/BUILD/4ca51307b106213ce7ad18dea3427170d8d6aafc-latest/log
/sw/slc9_x86-64/YODA/yoda-2.1.0-6/include/YODA/highfive/H5Object.hpp:13:10: fatal error: H5Ipublic.h: No such file or directory
make[3]: *** [Makefile:563: libRivetCore_la-Run.lo] Error 1
make[3]: *** Waiting for unfinished jobs....
/sw/slc9_x86-64/YODA/yoda-2.1.0-6/include/YODA/highfive/H5Object.hpp:13:10: fatal error: H5Ipublic.h: No such file or directory
/sw/slc9_x86-64/YODA/yoda-2.1.0-6/include/YODA/highfive/H5Object.hpp:13:10: fatal error: H5Ipublic.h: No such file or directory
make[3]: *** [Makefile:633: libRivetCore_la-AnalysisHandler.lo] Error 1
make[3]: *** [Makefile:612: libRivetCore_la-Analysis.lo] Error 1
/sw/slc9_x86-64/YODA/yoda-2.1.0-6/include/YODA/highfive/H5Object.hpp:13:10: fatal error: H5Ipublic.h: No such file or directory
make[3]: *** [Makefile:619: libRivetCore_la-AnalysisLoader.lo] Error 1
make[2]: *** [Makefile:659: all-recursive] Error 1
make[1]: *** [Makefile:567: all-recursive] Error 1
make: *** [Makefile:578: all-recursive] Error 1

Full log here.

[alibuild]

Error while checking build/O2/fullCI_slc9 for 9ffb681 at 2025-07-16 15:16:

No log files found

Full log here.