LERM tipping point detection

[CommonClimate]

Look into automating @alexkjames 's approach to tipping point detection, as implemented in his [LERM paper}(https://alexkjames.github.io/Detecting_Paleoclimate_Transitions_with_LERM/notebooks/Main_Analysis/IceCore_LERM.html). The function detect_transitions() from this notebook should be folded into Ammonyte under an appropriate name (making it clear that it is using LERM).

Same checklist as usual:

• attach methods to the Ammonyte series class
• create functionalities to plot and export results
• ask Claude to create detailed docstrings in the Pyleoclim style (using the Jupyter-execute decorator), using the NGRIP example
• create a Jupyter notebook (under /notebooks) that applies this to the entire NGRIP record (not just the Holocene)

[CommonClimate]

addressed by #11