Support uint constants

[pi8027]

TODOs:

• implement the same feature in ring and field,
• double-check Strategy expand declarations, and
• investigate the issue that the proof of vcgen_25 is not very fast.

cc: @proux01

[pi8027]

Lemma vcgen_25 ...
Proof.
move=> *.
Time lra. (* Finished transaction in 4.308 secs (3.801u,0.007s) (successful) *)
Restart.
Time lra. (* Finished transaction in 0.57 secs (0.552u,0.s) (successful) *)
Qed.

This is exactly the issue I pointed out in #54 (comment). I will fix it in a separate PR.

[pi8027]

TODOs have been addressed. Let's merge.

[pi8027]

Lemma vcgen_25 ...
Proof.
move=> *.
Time lra. (* Finished transaction in 4.308 secs (3.801u,0.007s) (successful) *)
Restart.
Time lra. (* Finished transaction in 0.57 secs (0.552u,0.s) (successful) *)
Qed.

This is exactly the issue I pointed out in #54 (comment). I will fix it in a separate PR.

I implemented the proposed solution (#74), but it does not fix the issue. The significant slowdown comes from coq.typecheck. I guess that coq.typecheck can be very slow in the presence of many large hypotheses. Does it explain the issue? @gares