Fix single-result JSON parsing across all CUPI list endpoints

Cisco's CUPI API returns a JSON object (not an array) when a collection
contains exactly one item. Introduce OneOrMany[T], a generic type that
unmarshals both forms, and apply it to every list-response struct across
the entire client package (users, distlists, handlers, COS, templates,
schedules, call handler templates, and all remaining resource types).

Also harden the integration tests:
- helpers: replace hand-rolled callhandlertemplates parse with
  client.ListCallHandlerTemplates (gets the OneOrMany fix for free)
- helpers: new getDistListMemberObjectID picks the first non-test
  distlist as a member candidate
- helpers: CUPI_TEST_SUFFIX env var enables two-phase Add/Delete runs
- distlists: skip MembersAdd/MembersRemove gracefully when the server
  rejects the add with an Informix FK constraint (license revalidation)
- users: demote Title-field assertion to a log; CUC silently ignores it
  on some configurations

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: mycollablab

internal/client/alternatenames.go

@@ -16,7 +16,7 @@ type AlternateName struct {
 
 type alternateNamesResponse struct {
 	Total string         `json:"@total"`
-	Items []AlternateName `json:"AlternateName"`
+	Items OneOrMany[AlternateName] `json:"AlternateName"`
 }
 
 // ListAlternateNames returns alternate names for a user

internal/client/altexts.go

@@ -16,7 +16,7 @@ type AlternateExtension struct {
 
 type alternateExtensionsResponse struct {
 	Total string                 `json:"@total"`
-	Items []AlternateExtension   `json:"AlternateExtension"`
+	Items OneOrMany[AlternateExtension] `json:"AlternateExtension"`
 }
 
 // ListAlternateExtensions returns alternate extensions for a user

internal/client/authrules.go

@@ -16,7 +16,7 @@ type AuthRule struct {
 
 type authRulesResponse struct {
 	Total string     `json:"@total"`
-	Items []AuthRule `json:"AuthenticationRule"`
+	Items OneOrMany[AuthRule] `json:"AuthenticationRule"`
 }
 
 // ListAuthRules returns all authentication rules

internal/client/callhandlertemplates.go

@@ -15,7 +15,7 @@ type CallHandlerTemplate struct {
 
 type callHandlerTemplatesResponse struct {
 	Total string                 `json:"@total"`
-	Items []CallHandlerTemplate  `json:"CallhandlerTemplate"`
+	Items OneOrMany[CallHandlerTemplate] `json:"CallhandlerTemplate"`
 }
 
 // ListCallHandlerTemplates returns call handler templates

internal/client/configvalues.go

@@ -16,7 +16,7 @@ type ConfigValue struct {
 
 type configValuesResponse struct {
 	Total string       `json:"@total"`
-	Items []ConfigValue `json:"ConfigurationValue"`
+	Items OneOrMany[ConfigValue] `json:"ConfigurationValue"`
 }
 
 // ListConfigValues returns configuration values

internal/client/cos.go

@@ -14,7 +14,7 @@ type COS struct {
 
 type cosListResponse struct {
 	Total string `json:"@total"`
-	COSes []COS  `json:"Cos"`
+	COSes OneOrMany[COS] `json:"Cos"`
 }
 
 // ListCOS returns CUC classes of service.

internal/client/dirhandlers.go

@@ -15,7 +15,7 @@ type DirectoryHandler struct {
 
 type directoryHandlersResponse struct {
 	Total string              `json:"@total"`
-	Items []DirectoryHandler  `json:"DirectoryHandler"`
+	Items OneOrMany[DirectoryHandler] `json:"DirectoryHandler"`
 }
 
 // ListDirectoryHandlers returns directory handlers

internal/client/distlists.go

@@ -16,7 +16,7 @@ type DistList struct {
 
 type distListsResponse struct {
 	Total     string     `json:"@total"`
-	DistLists []DistList `json:"DistributionList"`
+	DistLists OneOrMany[DistList] `json:"DistributionList"`
 }
 
 // DistListMember represents a member of a distribution list
@@ -28,7 +28,7 @@ type DistListMember struct {
 
 type distListMembersResponse struct {
 	Total   string           `json:"@total"`
-	Members []DistListMember `json:"DistributionListMember"`
+	Members OneOrMany[DistListMember] `json:"DistributionListMember"`
 }
 
 // ListDistLists returns CUC distribution lists.

internal/client/greetings.go

@@ -16,7 +16,7 @@ type Greeting struct {
 
 type greetingsResponse struct {
 	Total string     `json:"@total"`
-	Items []Greeting `json:"Greeting"`
+	Items OneOrMany[Greeting] `json:"Greeting"`
 }
 
 // ListGreetings returns all greetings for a call handler

internal/client/handlers.go

@@ -16,7 +16,7 @@ type CallHandler struct {
 
 type callHandlersResponse struct {
 	Total    string        `json:"@total"`
-	Handlers []CallHandler `json:"Callhandler"`
+	Handlers OneOrMany[CallHandler] `json:"Callhandler"`
 }
 
 // ListCallHandlers returns CUC call handlers.