Cosmwasm@V3

## Goal
With the latest release of the core Cosmwasm libraries, we can upgrade this library to the latest version.

## Context
Most changes to this major version upgrade are straightforward, however there are a few crucial design decisions to make in order to upgrade these crates. Specifically:

- `Coin` struct in cosmwasm now uses **Uint256** for its *amount* value. We must decide if we update all balance related objects in this library from Uint128 to Uint256, including contract message types and internal states.

I have a first pass at the migration with full passing test [here](https://github.com/permissionlessweb/cw-plus/pull/2),which do replace most Uint128 expectations with Uint256. NOTE: `cw4-stake` does not have Uint128 updated to Uint256 in this demo , due to the way the `calc_weight` function was implemented in this demo. This function expects to return a u64 value from division of a users stake and tokens per weight, and to prevent a scenario where the result of this arithmetic with Uint256 is > u64::MAX, this crate still uses Uint128.

I would love to hear how others view this migration should be implemented! This crate is heavily relied on in various contract in the ecosystem, so lets get this upgraded! ::)

Start by reviewing the migration described in the linked pull request and the balance-related types affected by the CosmWasm upgrade. Pay particular attention to the `cw4-stake` crate and its `calc_weight` function, which still uses Uint128. Done requires agreeing on the Uint128-to-Uint256 scope, including contract messages and internal state, then validating the migration with the project’s passing tests.

Written by the indexing model from the issue text.