Add CBOR support for BigInteger and BigDecimal types

[AmitKulkarni23]

Problem

BigInteger and BigDecimal types currently fail at codegen time when used with CBOR protocol.

Specification Requirements

According to the Smithy RPC v2 CBOR spec:

• BigInteger: Should use Major Type 6, tags 2 (unsigned bignum) or 3 (negative bignum)
• BigDecimal: Should use Major Type 6, tag 4 (decimal fraction)

Current State

• aws-smithy-cbor doesn't expose methods for these CBOR tags
• The underlying minicbor library supports tags (used internally for timestamps)
• Codegen currently fails with an error when BigInteger/BigDecimal are used with CBOR

Related

• PR Add support for Smithy bigInteger and bigDecimal types as string wrappers in aws-smithy-types, allowing users to parse with their preferred big number library. #4418 - Initial BigInteger/BigDecimal implementation