Properly handle BigInt <-> JSON

[brendanrbrown]

We need to serialize BigInt values to JSON in the offchain code. However, BigInt is not supported in JSON, and the standard JavaScript conversions via parse or stringify fail either with runtime exceptions or by silently overflowing.

For now, TrustlessSidechain.Utils.Codecs.bigIntCodec throws an exception when attempting to serialize a value that is out of the range of a PureScript Int.

We can probably do better using an existing JavaScript package like this one for serializing BigInt.

Or, we could reconsider the use of BigInt in the first place for values that need to be serialized to JSON.

For some details see https://github.com/input-output-hk/trustless-sidechain/pull/711#discussion_r1510989411

and the code Note [BigInt values and JSON].

This issue is moot if we move the offchain code to Haskell, as discussed here: https://github.com/input-output-hk/trustless-sidechain/discussions/710

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IOG Jira: https://input-output.atlassian.net/browse/ETCM-6865