This commit brings support for multiple secret keys in the TFHE
dialect. In particular, a parameterized `TFHE` circuit can now be
given as input, with any combination of (semantically valid) of
ks/bs/woppbs mixing different secret keys, and compiled down to a
valid executable function, with server keys properly looked up.
Secret keys are now stateful objects which can be:
-> none/unparameterized (syntax `sk?`): The keys are in state after
the lowering from the `FHE` dialect.
-> parameterized (syntax `sk<identifier, polysize, dimension>`): The
keys were parameterized, either by user or by the optimizer. The
`identifier` field can be used to disambiguate two keys with same
`polysize` and `dimension`.
-> normalized (syntax `sk[index]<polysize, dimension>`): The keys were
attached to their index in the list of keys in the runtime context.
The _normalization_ of key indices also acts on the ksk, bsk and pksk,
which are given indices in the same spirit now.
Finally, in order to allow parameterized `TFHE` circuit to be given
as input and compiled down to executable functions, we added a way to
pass the encodings that are used to encode/decode the circuit
inputs/outputs. In the case of a compilation from the `FHE` dialect,
those informations are automatically extracted from the higher level
informations available in this dialect.
With TFHE operations becoming batchable, the batching pass must now be
run after the conversion to TFHE,and TFHE parametrization, but before
any further lowering.
