ICS-721 Implementation (Golang)

Files: - `types/trace.go` Commits: - [`cfc058309adcf73478d3828a524ecf8e546420ed`](https://github.com/bianjieai/nft-transfer/tree/cfc058309adcf73478d3828a524ecf8e546420ed) - [`87cdf3b7dd969237c9ffc8e056bfc24cab5e2bba`](https://github.com/bianjieai/nft-transfer/tree/87cdf3b7dd969237c9ffc8e056bfc24cab5e2bba) - [`fa7bd3f3cb1ebe24f781953a781add96509b4c2a`](https://github.com/bianjieai/nft-transfer/tree/fa7bd3f3cb1ebe24f781953a781add96509b4c2a) The `rawClassID` is converted to class trace by splitting with the separator `/` in the function `ParseClassTrace()`, which creates a new string slice of `classSplit`. The `Path` and `BaseClassId` are determined by the position in the string slice. ```go=67 func ParseClassTrace(rawClassID string) ClassTrace { classSplit := strings.Split(rawClassID, "/") if classSplit[0] == rawClassID { return ClassTrace{ Path: "", BaseClassId: rawClassID, } } return ClassTrace{ Path: strings.Join(classSplit[:len(classSplit)-1], "/"), BaseClassId: classSplit[len(classSplit)-1], } } ``` It works fine if there is no "/" in the input, `rawClassID`. In case that the `rawClassID` contains "/", it could be an issue with this splitting method. For example, the following class trace parsing could occur: > e.g. "class-1/2" => ClassTrace{Path: "class-1", BaseClassId: "2"} which would impact the following usage of the class trace and lead to the collision of class trace afterwards. Note that there is no restriction in the ADR nft modules in [`ADR-043`](https://github.com/cosmos/cosmos-sdk/blob/main/docs/architecture/adr-043-nft-module.md#nft). Additionally, it should not restrict the classID with "/", because the `voucherClassID` could be constructed with prefix `ibc/` during the interchain NFT transfer. Then the voucher NFT will be minted in the upper level NFT modules. **Reference**: - https://github.com/cosmos/cosmos-sdk/blob/main/docs/architecture/adr-043-nft-module.md#nft