Support for array as argument to FenwickTree#new

[universato]

• Tests pass
• Appropriate changes to README are included in PR

I've made it so that FenweickTree#new can take an array as an argument.

new(int): 292ms
https://atcoder.jp/contests/practice2/submissions/22893243

new(array): 268ms
https://atcoder.jp/contests/practice2/submissions/22895055

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[universato]

@googlebot I signed it!

[hakatashi]

Great! Thank you for your contribution 🥰