BBH ID: compute initial orbital params from PN

[nilsvu]

Proposed changes

Port parts of SpEC's ZeroEccParamsFromPN.py to set initial orbital parameters for circular orbits. Two functions from SpEC are just imported, and should be modernized later. This allows to generate near-circular ID like this:

spectre bbh generate-id -o ./test -q 1 --chi-A 0 0 0 --chi-B 0 0 0 --eccentricity 0 --num-orbits 20

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Further comments

[nilsdeppe]

LGTM! A few minor suggestions that I'm not sure are reasonable. Please squash if you decide to do them!

[nilsdeppe]

While adding these, I'm not sure how much of an effect tidal deformability has for including matter terms. @moble @ffoucart do you know what SpEC does for NSNS initial parameters? Just assume BHs?

[ffoucart]

The main difference would be in the estimated number of orbits to merger. The current initial data just uses the BBH formula at a fixed distance. We do have an estimate of the number of orbits that includes some correction from the BBH formula, but I don't recall whether it's used at all in current automation. @tiamartineau would know.

[nilsdeppe]

Alright, thank you! I'm just curious for the future, I don't think this should be worried about in this PR.

[tiamartineau]

...ah, ignore my first comment, thought you were talking about the orbits to eccentricity reduction, not merger-- the answer is no, not yet.

[nilsdeppe]

Okay, that's @tiamartineau !!

[nilsdeppe]

LGTM, though GCC has the tests failing. Please squash!