Optimize loadVolumes method using addVolume, addVolumeFromUrl methods

[jennydaman]

niivue-react/src/NiivueMutator.ts

Lines 101 to 110 in 6bd0a10

	/**
	* A wrapper for `Niivue.loadVolumes` which also handles bugs.
	* N.B.: `Niivue.loadVolumes` will _clear_ any currently loaded volume,
	* so to add new volumes it is necessary to pass old volumes as well.
	*/
	public async loadVolumes(volumes: NVRVolume[]) {
	await this.nv.loadVolumes(volumes.map(toLoadableVolume));
	volumes.forEach((volume) => this.handleSpecialImageProperties(volume));
	this.workaroundLoadVolumesColorbarBug(volumes);
	}

Currently, niivue-react only uses loadVolumes which unloads then reloads all volumes unnecessarily.