draft DHCP allocator abstraction

[soypat]

Addressing tinygo-org/espradio#51 (comment)

type Allocator interface {
	// Offer tentatively reserves a binding for the requesting client and
	// returns it. It is called when the server receives a DISCOVER/SOLICIT.
	Offer(Request) (Binding, error)
	// Commit binds a previously offered reservation, finalizing the lease, and
	// returns the committed binding. It is called when the server receives a
	// REQUEST.
	Commit(Request) (Binding, error)
	// Release frees the binding held for the given client identity. It is
	// called when the server receives a RELEASE. Releasing an unknown client is
	// not an error.
	Release(clientID []byte) error
	// Decline marks the addresses in the request as unusable, typically because
	// the client detected an address conflict. It is called when the server
	// receives a DECLINE.
	Decline(Request) error

	// AppendOptions lets the allocator customize the option bytes the server is
	// about to send. dst already contains the options the server derived from
	// its own configuration (server identifier, router, subnet mask, DNS, lease
	// times, ...) for the given client and binding. The implementation may
	// append further options, or rewrite the existing ones, and must return the
	// resulting slice. The returned slice must not exceed dst's capacity.
	AppendOptions(dst []byte, clientID []byte, b Binding) ([]byte, error)
}

[codecov]

Codecov Report

❌ Patch coverage is 67.88321% with 88 lines in your changes missing coverage. Please review.
✅ Project coverage is 59.28%. Comparing base (8f9d765) to head (b46b4c7).

Files with missing lines	Patch %	Lines
dhcp/dhcpv4/server.go	66.88%	36 Missing and 15 partials ⚠️
dhcp/dhcpv4/allocator.go	68.75%	24 Missing and 11 partials ⚠️
dhcp/lease.go	66.66%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #132      +/-   ##
==========================================
+ Coverage   59.17%   59.28%   +0.10%     
==========================================
  Files         104      106       +2     
  Lines       11664    11813     +149     
==========================================
+ Hits         6902     7003     +101     
- Misses       4041     4074      +33     
- Partials      721      736      +15     

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[MDr164]

Quickly glanced over it and already found a couple questionable items in this PR. Want me to review or rather wait until you moved it out of draft?

[soypat]

As you wish, this PR is pure clankerspeak. I'll eventually take a more in depth look, just wanted to get it out there so I could see diff comfortably