Do not replace building_block_v2 when inputs change

[grubmeshi]

Problem

When a user changes any input value on a meshstack_building_block_v2 resource, Terraform plans a full destroy + create cycle because:

1. The inputs map has a RequiresReplace plan modifier (building_block_common.go:56)
2. The resource's Update method unconditionally returns an error: "Building blocks can't be updated" (building_block_v2_resource.go:315)

This is because the meshBuildingBlock meshObject API (POST/DELETE only) does not support PUT/PATCH — there is no way to update inputs on an existing building block via the current API.

Impact

Destroying and recreating a building block on every input change:

• Loses the building block's run history and outputs
• Triggers an unnecessary delete run followed by a create run
• Can cause downtime for dependent infrastructure managed by the building block runner
• Breaks parent/child building block relationships that reference the old UUID

Proposed fix

This will be addressed by the new meshstack_building_block_v3 resource, which should support in-place input updates by triggering a new building block run rather than replacing the entire building block. This likely requires a corresponding API change in meshStack to support updating building block inputs (or a dedicated "retrigger run" mechanism).