feat(lib): define v1 blob types for feature lists and diffs

[jcscottiii]

Introduces the version 1 data contracts for two new blob types:

• FeatureList: Represents the full state of a feature search result at a point in time.

• FeatureListDiff: Represents the delta between two feature list snapshots, capturing added, removed, modified, moved, and split features. Additonally, added some helpers that will be useful in the future.

Note: Some of these changes already exist in

webstatus.dev/workers/event_producer/pkg/differ/types.go

Lines 174 to 225 in 61f8e16

	// Sort orders all slices deterministically by Name (primary) and ID (secondary).
	// This ensures stable JSON output and organized UI/Email lists.
	func (d *FeatureDiff) Sort() {
	sort.Slice(d.Added, func(i, j int) bool {
	if d.Added[i].Name != d.Added[j].Name {
	return d.Added[i].Name < d.Added[j].Name
	}
	return d.Added[i].ID < d.Added[j].ID
	})
	sort.Slice(d.Removed, func(i, j int) bool {
	if d.Removed[i].Name != d.Removed[j].Name {
	return d.Removed[i].Name < d.Removed[j].Name
	}
	return d.Removed[i].ID < d.Removed[j].ID
	})
	sort.Slice(d.Modified, func(i, j int) bool {
	if d.Modified[i].Name != d.Modified[j].Name {
	return d.Modified[i].Name < d.Modified[j].Name
	}
	return d.Modified[i].ID < d.Modified[j].ID
	})
	sort.Slice(d.Moves, func(i, j int) bool {
	if d.Moves[i].FromName != d.Moves[j].FromName {
	return d.Moves[i].FromName < d.Moves[j].FromName
	}
	return d.Moves[i].FromID < d.Moves[j].FromID
	})
	sort.Slice(d.Splits, func(i, j int) bool {
	if d.Splits[i].FromName != d.Splits[j].FromName {
	return d.Splits[i].FromName < d.Splits[j].FromName
	}
	return d.Splits[i].FromID < d.Splits[j].FromID
	})
	// Also sort the targets within a Split
	for k := range d.Splits {
	to := d.Splits[k].To
	sort.Slice(to, func(i, j int) bool {
	if to[i].Name != to[j].Name {
	return to[i].Name < to[j].Name
	}
	return to[i].ID < to[j].ID
	})
	}
	}

. But to prevent too many changes at once, they will be removed in the future.

These types define the schema for data that will be persisted in blob storage.

Part of #2107

Split up of #2106