beacon-wasm: use the builtin serde feature provided by wasm-bindgen

beacon, beacon-wasm: fix incorrect example block and remove f64 parsing for uint

wasm: fix U1099511627776 exceeding u32 limit

dep: update bm-le to 0.10

beacon-wasm: webassembly-compiled beacon state transition function

srml-casper: introduce epoch number

srml-casper: implement slashing conditions

Casper consensus in SRML

Embed all yamltests in CI and Rust tests

Directly put everything under test cfg

In v0.8, deposit proof are with an additional depth of length mix, but our current proof generation code didn't handle it. This PR generates the additional depth proof and makes the blockchain client able to build blocks and submit attestations.