fix: update max lengths and check r2 bcast commit length

[milapsheth]

• Updated max msg lengths based on the improved big number encoding. ZenGo-X/rust-gmp was also serializing the big num as a hex string which takes twice as much space. After the fix from axelarnetwork/unknown_order#3, we take half as much space for all messages.
• Updated bincode version and switched to using varint encoding. This avoids encoding length of each vector with 8 bytes (instead it uses as much as needed, which is usually one or two bytes). Note that the deserialize function uses a different default than the DefaultOptions
• Added a length check for the r2::Bcast variable-sized message. Also, max keygen msg length suffices for this message upto threshold of 100 #171
• Misc: switched to using x.y for all crate versions.

[milapsheth]

@ggutoski Run cargo update locally to update the paillier-rs dependency. When running the integration test, I get the following message sizes:

integration::single_thread: total_share_count 10, threshold 5
 integration::single_thread: keygen...
 integration::single_thread::execute: round 1 bcast byte length 4267
 integration::single_thread::execute: round 2 bcast byte length 243
 integration::single_thread::execute: round 2 p2p byte length 526
 integration::single_thread::execute: round 3 bcast byte length 72
 integration::single_thread: sign...
 integration::single_thread::execute: round 1 bcast byte length 557
 integration::single_thread::execute: round 1 p2p byte length 1755
 integration::single_thread::execute: round 2 p2p byte length 6828
 integration::single_thread::execute: round 3 bcast byte length 173
 integration::single_thread::execute: round 4 bcast byte length 73
 integration::single_thread::execute: round 5 bcast byte length 40
 integration::single_thread::execute: round 5 p2p byte length 1789
 integration::single_thread::execute: round 6 bcast byte length 175
 integration::single_thread::execute: round 7 bcast byte length 40
test single_thread::basic_correctness ... ok

[milapsheth]

Going offline, so feel free to merge if it looks good!