Typesafe library

[dapplion]

• Use same Typescript and lint options as Lodestar monorepo
• Use same Typescript version as Lodestar monorepo

Those two changes have surfaced many issues which I've resolved as many as possiible. @wemeetagain I don't know how to handle the function calls that you do with null such as

ssz/src/types/composite/abstract.ts

Line 103 in 36b30f8

if (!this.hasVariableSerializedLength() && length !== this.struct_getSerializedLength(null)) {

please take a look and find a solution accepted by the Typescript compiler.

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2. This PR also enforces correct types for ContainerType fields and ArrayType element type. See this test as an example of what compiles and what doesn't now
   https://github.com/ChainSafe/ssz/blob/36b30f8916/test/unit/eth2Types.test.ts

3. Replaced the toHexString and fromHexString for simpler alternatives that are

• toHexString: x12 faster (now 0.4 µs / op, 32 bytes input)
• fromHexString: x2 faster (now 2.4 µs / op, 32 bytes input)

[wemeetagain]

struct_getSerializedLength is called with null in cases where the type is "fixed-length" and not dependent on the value.
I think @3xtr4t3rr3str14l ran into this same issue in #96

The issue is that the signature is different between fixed-length and variable-length types.
One naive approach could be to change the signature to struct_getSerializedLength(value?: T): number.
And just throw an error at runtime if the value isn't provided for variable-length types.

A different approach could be to cast null/undefined to T in the fixed-length type case.

[wemeetagain]

change the signature to struct_getSerializedLength(value?: T): number.

Seems we already did similar here in #110 https://github.com/ChainSafe/ssz/pull/110/files#diff-f7dbd702062a823eb1050e5721c8802d7d613821a719d69da838bc0760cef64bR594-R596

Pushed a few commits on top to fix conflicts and type errors

[dapplion]

conflicts

[dapplion]

@wemeetagain Can you take a look?

[wemeetagain]

🚀 LGTM, we should link against lodestar and ensure there's no critical errors

[dapplion]

PR got fucked with conflicts 😅 @wemeetagain do you think it's worth it to pursue this?

[dapplion]

Implemented with #223