make log_quasitriu always take at least one sqrt

[oscardssmith]

seems to fix #54833 (although it's not a fully principled fix, I just think this might have been an edge-case neglected in the original paper, that said, it also possibly is a problem with m>4 that is independent of the number of sqrts we take).

Before:

julia> qtriu = [0.9950041652780259 -0.09983341664682815 0.07153667745275474; 0.09983341664682804 0.9950041652780259 0.06981527929449967; 0.0 0.0 1.0]
#before
julia> exp(log(qtriu)) - qtriu
3×3 Matrix{Float64}:
 1.11022e-16  1.38778e-17  -0.00269465
 0.0          1.11022e-16   0.00260462
 0.0          0.0           0.0
 #after
 3×3 Matrix{Float64}:
 1.11022e-16  1.38778e-17  3.99319e-13
 0.0          1.11022e-16  3.8973e-13
 0.0          0.0          0.0

This still needs tests.

[dkarrasch]

Interestingly, the scipy version doesn't seem to have this IIUC: https://github.com/scipy/scipy/blob/628a6b3bf3e1a3149b8a6390322ae976bba930fa/scipy/linalg/_matfuncs_inv_ssq.py#L367-L377

[oscardssmith]

Ah, that is a very useful resource. We should definitely check that out to see what the correct params are.