[ENH,BUG] added weighted elastic barycenter and fix cache issue in subgradient method

[maxwell1503]

Reference Issues/PRs

Solve #1251

What does this implement/fix? Explain your changes.

• Added weighted version of elastic barycenter by adding an optional parameter (weights, by default equals to ones)
• Fixed the cache issue in sub gradient method by making a copy of barycenter

Does your contribution introduce a new dependency? If yes, which one?

No

Any other comments?

No

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Thank you for contributing to aeon

I have added the following labels to this PR based on the title: [ $\color{#d73a4a}{\textsf{bug}}$, $\color{#FEF1BE}{\textsf{enhancement}}$ ].
I have added the following labels to this PR based on the changes made: [ $\color{#4011F3}{\textsf{clustering}}$ ]. Feel free to change these if they do not properly represent the PR.

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[chrisholder]

Great addition thanks so much!

[TonyBagnall]

great, thanks