Remove useless Codable requirement

[arnauddorgans]

The PR removes useless Codable requirements

[bsneed]

can you elaborate on why you needed to make this change, or was it purely for correctness?

[arnauddorgans]

@bsneed it forces us to write useless Decodable conformances on objects that are not decodable
e.g.

extension AnalyticsClient {
    struct Context: Codable {
        let value: Any
        let encode: (inout SingleValueEncodingContainer) throws -> Void

        init<T: Encodable>(_ value: T) {
            self.value = value
            self.encode = { try $0.encode(value) }
        }

        init(from decoder: any Decoder) throws {
            // Waiting for https://github.com/segmentio/analytics-swift/pull/386 to me merged
            throw DecodingError.dataCorrupted(.init(
                codingPath: decoder.codingPath,
                debugDescription: "Decodable is not used"
            ))
        }

        func encode(to encoder: any Encoder) throws {
            var container = encoder.singleValueContainer()
            try encode(&container)
        }
    }
}