Change default geometry to run1_a

[brownd1978]

This is a breaking, non-backwards-compatible change advancing the default simulation geometry from that used in MDC2020 datasets to that expected for run1 (run1_a scenario), which will be used in the next round of simulation (MDC2025). After this is meged, the legacy MDC2020 geometry must be explicitly used to analyze MDC2020 datasets, or to create new MDC2020 datasets. This will be 'automatic' for people working in MDC2020 SimJob musings, provided they are running scripts from Production.

[FNALbuild]

Hi @brownd1978,
You have proposed changes to files in these packages:

• Mu2eG4

which require these tests: build.

@Mu2e/write, @Mu2e/fnalbuild-users have access to CI actions on main.

The following users requested to be notified about changes to these packages:
@resnegfk

⌛ The following tests have been triggered for c045819: build (Build queue - API unavailable)

About FNALbuild. Code review on Mu2e/Offline.

[FNALbuild]

☔ The build tests failed for c045819.

Test	Result	Details
test with	✅	Command did not list any other PRs to include
merge	✅	Merged c045819 at c949696
build (prof)	✅	Log file. Build time: 04 min 37 sec
ceSimReco	❌	Log file. Return Code 1.
g4test_03MT	❌	Log file. Return Code 1.
transportOnly	❌	Log file. Return Code 1.
POT	❌	Log file. Return Code 1.
g4study	✅	Log file.
cosmicSimReco	❌	Log file. Return Code 1.
cosmicOffSpill	❌	Log file. Return Code 1.
ceSteps	❌	Log file. Return Code 1.
ceDigi	❌	Log file. Return Code 24.
muDauSteps	❌	Log file. Return Code 1.
ceMix	❌	Log file. Return Code 24.
rootOverlaps	❌	Log file. Return Code 1.
g4surfaceCheck	❌	Log file. Return Code 1.
trigger	❌	Log file. Return Code 2.
check_cmake	✅	Log file.
FIXME, TODO	✅	TODO (0) FIXME (0) in 0 files
clang-tidy	✅	0 errors 0 warnings
whitespace check	✅	no whitespace errors found

N.B. These results were obtained from a build of this Pull Request at c045819 after being merged into the base branch at c949696.

For more information, please check the job page here.
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[rlcee]

missing closing quote