Some progress on verifier

[weikengchen]

This PR made a few optimization as well as kickstarted the end-to-end implementation of a verifier.

• many "push_" functions in the gadgets have been moved into the Pushable trait. Now, one can simply push it.
• finish most of the components of a verifier, except the part for checking commitment opening and FRI.

[weikengchen]

Additional changes may be added to this PR. This PR is here to notify potential refactoring and avoid collisions.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 97.21254% with 8 lines in your changes missing coverage. Please review.

Files	Coverage Δ
src/air/mod.rs	100.00% <100.00%> (ø)
src/channel/bitcoin_script.rs	90.76% <ø> (-1.13%)	:arrow_down:
src/channel/mod.rs	94.64% <100.00%> (+1.30%)	:arrow_up:
src/constraints/bitcoin_script.rs	100.00% <ø> (ø)
src/fibonacci/bitcoin_script/composition.rs	100.00% <100.00%> (ø)
src/fibonacci/bitcoin_script/mod.rs	100.00% <100.00%> (ø)
src/fri/bitcoin_script.rs	100.00% <100.00%> (ø)
src/lib.rs	100.00% <100.00%> (ø)
src/merkle_tree/bitcoin_script.rs	100.00% <ø> (ø)
src/merkle_tree/mod.rs	100.00% <100.00%> (ø)
... and 8 more

[weikengchen]

Now the only remaining part is about FRI as well as commitment opening. Since this PR is too heavy already, I think it is time to conclude this PR for review.