Introduce getters for components of a QuasiNewtonModel #321

Job	Run time
Julia lts - macos-latest - x64 - push	8m 35s
Julia 1 - macos-latest - x64 - push	14m 30s
Julia 1 - ubuntu-latest - x64 - push	9m 39s
Julia 1 - macos-latest - arm64 - push	8m 19s
Julia 1 - macos-15-intel - x64 - push	10m 24s
Julia lts - ubuntu-latest - x64 - push	6m 8s
Julia 1 - ubuntu-24.04-arm - arm64 - push	8m 27s
Julia pre - macos-latest - x64 - push	12m 4s
Julia lts - windows-latest - x64 - push	6m 46s
Julia pre - ubuntu-latest - x64 - push	8m 0s
Julia 1 - windows-latest - x64 - push	11m 30s
Julia lts - macos-15-intel - x64 - push	6m 7s
Julia pre - windows-latest - x64 - push	9m 51s
	2h 0m 20s

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