`tokenMetadata` should have valid data

[DevLubab]

If a user mint a token with empty tokenMetadata it will still mint. I think this can cause some unexpected problems and need to validate it before storing it

The test below should pass

contracts/near-workspaces/__tests__/nft.ava.ts

Lines 82 to 89 in c71e2a8

	/** @todo fix in the contract **/
	// await test.throwsAsync(async () => {
	// await call_mint(contract, alice, {
	// tokenMetadata: {},
	// token_royalty: TOKEN_ROYALTY
	// })
	// })
	// test.log(`✓ Alice failed to mint without tokenMetadata\n`)

[bestatigen]

Let's add a token_metadata_is_sane function assert and token_royatly_is_sane to mint function:

assert(token_metadata_is_sane((tokenMetadata), 'Token doesn't have valid Metadata')
assert(token_metadata_is_sane((tokenRoyalty), 'Token doesn't have valid Royalty')