Allow save/load of polynomial coefficients about metalibm HOT 2 OPEN

[Request for Comment]
The idea will be to have a format containing: a list of polynomial approximations

Each approximation would be uniquely identified by

• formal approximated function expression
• approximation range
• degree
• coefficient formats
• error bound
• forced odd / forced even / no constraint

Each approximation would be stored as an indexed map of numerical coefficients

from metalibm.

approximated_fct: exp(x)
type: piecewise_polynomial_uniform_deg
approximation_range: Interval(0, 1)
error_target: dar(2**-25)
approximation:
  - step: 
      sub_approx_range: [0, 0.5]
      sub_approx: Polynomial([0, 1])

from metalibm.