implement `(he|sy)ev`, `(he|sy)evd` lapack routines for hermitian/symmetric eigendecomposition

also, we should add the `linalg.eigen` op to unify them

unlike the QR, the format is unique so we should be able to write one diff rule

also, we should consider specialized routines like `spev`, `{hb,sb}ev`, `stev`, `stevd`, ...

Start by reviewing open pull request #1941 and the requested `(he|sy)ev` and `(he|sy)evd` LAPACK routines. Check how `linalg.eigen` and a unified differentiation rule should cover them; done means the requested routines and operation are implemented, while specialized routines remain a consideration.

Written by the indexing model from the issue text.