Remove int decoding option, support bigint by default

[jasonpaulos]

Remove the IntDecoding enum option on REST API calls. This option was originally introduced to allow bigints to be decoded by the REST API in a backwards-compatible way, but it's no longer needed in v3.

Instead, we should decode with support for bigints by default (either by upgrading every int to a bigint or only those which exceed Number.MAX_SAFE_INTEGER). The algod and indexer REST API specs should indicate which fields actually need to be represented by a uint64 or larger with the "x-algorand-format": "uint64" value; these can be typed as bigint by this SDK, and the rest can remain numbers.