Set `eager=true` in `exponentiate` backend

[mtfishman]

In ITensorTDVP.jl v0.3, we set eager=true by default when using the KrylovKit.exponentiate solver/updater, while in ITensorTDVP.jl v0.4 we don't override the default that KrylovKit.jl sets, which is eager=false. This can potentially have big performance penalties since it can lead to many unnecessary applications of the reduced operator.

See:

• https://jutho.github.io/KrylovKit.jl/stable/man/matfun/#KrylovKit.exponentiate
• https://itensor.discourse.group/t/newer-version-of-tdvp-seems-to-be-much-slower/2061
• ITensorTDVP.jl v0.4 ITensorTDVP.jl#74

For users hitting this issue who are using ITensorTDVP.jl v0.4, you can manually pass updater_kwargs=(; eager=true) to tdvp to get the same (more efficient) behavior of ITensorTDVP.jl v0.3.