Add `SolverCore.reset!(solver)` #157

Job	Run time
Julia nightly - ubuntu-latest - x64 - pull_request	2m 13s
Julia 1 - windows-latest - x64 - pull_request	2m 19s
Julia 1.6 - windows-latest - x64 - pull_request	13m 40s
Julia 1.6 - macOS-latest - x64 - pull_request	4m 14s
Julia nightly - macOS-latest - x64 - pull_request	3m 43s
Julia 1 - ubuntu-latest - x64 - pull_request	1m 57s
Julia 1.6 - ubuntu-latest - x64 - pull_request	2m 35s
Julia nightly - windows-latest - x64 - pull_request	2m 42s
Julia 1 - macOS-latest - x64 - pull_request	3m 50s
	37m 13s

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