feat(PhyslibAlpha): speed limit of the open tight binding chain

[naype888-cloud]

hey Joseph, hey TimeRoot, hello fellas! this one is the speed limit, it uses the Mandelstam-Tamm bridge you just merged (#1711), thanks a lot for that one, so i'm keeping my word on Robertson-Cramer Rao-Mandelstamm-Tamm inside the same basquet.
TightBindingChain/SpeedLimit.lean, 219 lines, builds on #1711 and the maximal current state (#1716), both merged, no open dependencies.
the idea: for t != 0 the current eigenstates carry different currents, so normalized they make an orthonormal basis. every current is at most maxCurrent = 2|a t| cos(pi/(N+1)), so no state, pure or mixed, can move faster than that, and the maximal current state hits the bound exactly.

1. currentBasis: the orthonormal basis of normalized current eigenstates.
2. re_inner_current_eq_sum: re <psi|J|psi> = sum lambda_k |<k|psi>|^2 in that basis.
3. abs_currentEigenvalue_le: |2 a t cos(k pi/(N+1))| <= maxCurrent for 1 <= k <= N.
4. expectation_current_maxCurrentState: = 2 a t cos(pi/(N+1)) in the maximal current state.
5. abs_expectation_current_le: || <= maxCurrent in every state.
6. abs_expectation_current_maxCurrentState: the maximal current state moves exactly at maxCurrent.

have a nice day and im here, ready for any changes, thanks again for all the patience!

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