feat(PhyslibAlpha): elemental uncertainty of the open tight binding chain

[naype888-cloud]

Hi Joseph, hi TimeRoot, hello everyone!

Here is the next one — I'm moving as fast as I can, so thanks a lot for all the support 🙏

File: TightBindingChain/ElementalUncertainty.lean (145 lines). It sits directly on top of the saturation PR #1718, which is already merged, so there are no open dependencies.

Idea: In the maximal current state the energy and position fluctuations are uncorrelated, so Robertson–Schrödinger closes as an identity: the variance product is exactly the squared bracket plus the Gram defect.
Inside this PR what you get?:
covariance_maxCurrentState: Cov(H,X) = 0 in the maximal current state.
variance_mul_variance_maxCurrentState: Var(H) * Var(X) = (atcos(pi/(N+1)))^2 + defect.
CNava: the constant C_Nava = sqrt(Var(H) * Var(X)) / |atcos(pi/(N+1))|.
one_le_CNava, CNava_eq_one_iff, one_lt_CNava: C_Nava >= 1, =1 iff N=2,3, >1 from four sites on.

nava_robertson_schrodinger_elemental_dimensional_uncertainty_inequality: everything together in one statement

As always, happy to make any changes here or on Zulip!

[github-actions]

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