feat(spg & spgnft): add support for base URI

[sebsadface]

Description

This PR adds support for base URIs in SPG and SPGNFT. The baseURI is optional. If set, the tokenURI will be either baseURI + token ID (if nftMetadataURI is empty) or baseURI + nftMetadataURI. When baseURI is empty, the tokenURI will be the nftMetadataURI provided during minting.

Key Changes

• Added _baseURI storage to SPGNFT.
• Added baseURI, setBaseURI, and an internal _baseURI function in SPGNFT for setting and retrieving base URIs.
• Introduced an InitParam struct for SPGNFT to handle initialization parameters and avoid deep stack issues.
• Updated the initialize function in SPGNFT and createCollection function in SPG to use the new InitParam struct.
• Minor style and comment updates.

Tests

• Added test_SPGNFT_setBaseURI to cover setting and retrieving base URIs, testing combinations of empty and non-empty baseURI and nftMetadataURI.
• Updated existing tests to align with the changes in SPG and SPGNFT.

All tests (new and existing) pass locally.

Related Issue

• Closes BaseURI Support in SPGNFT #29

Notes

This PR introduces interface changes to the createCollection function in SPG and functions in SPGNFT.