pkg/net: add ip arithmetic functions

[takonomura]

To address #3142, I implemented a proof-of-concept API to perform arithmetic operations on IP addresses. Since this PR is a proof-of-concept, I welcome any feedback on naming conventions, interface design, or any other areas where improvements could be made.

This change introduces two functions for performing arithmetic operations on IP addresses and CIDR networks. These functions may be useful for use cases such as IP address management in CUE.

net.AddIPOffset

AddIPOffset adds a numerical offset to a given IP address.

This function is useful for automatically generating IP addresses for a large number of hosts, as demonstrated in the example below:

let networks = [
        "192.168.0.0/24",
        "2001:db8::/64",
]
for i in list.Range(1, 10, 1) {
        "testhost-\(i)": {
                interfaces: eth0: [for network in networks {net.AddIPOffset(network, i)}]
        }
}

net.AddIPCIDROffset

AddIPCIDROffset adds a numerical offset to a given CIDR subnet.

This function is useful for generating network prefixes based on specific rules, as demonstrated in the example below:

#VLAN: {
	id:     >=1 & <=4096
	prefix: net.AddIPCIDROffset("10.0.0.0/24", id)
}

vlanA: #VLAN & {id: 1}    // prefix: 10.0.1.0/24
vlanB: #VLAN & {id: 2}    // prefix: 10.0.2.0/24
vlanC: #VLAN & {id: 3}    // prefix: 10.0.3.0/24
vlanX: #VLAN & {id: 1000} // prefix: 10.3.232.0/24

[myitcv]

@takonomura thanks for raising this. We are extremely busy in the run up to KubeCon so please bear with us!