fix: replace moby/moby namesgenerator with internal implementation (#21377)

Replace the external moby/moby/pkg/namesgenerator dependency with an
internal implementation using gofakeit/v7. The moby package has ~25k
unique name combinations, and with its retry parameter only adds a
random digit 0-9, giving ~250k possibilities. In parallel tests, this
has led to collisions (flakes).

The new internal API at coderd/util/namesgenerator eliminates the
external dependnecy and offers functions with explicit uniqueness
guarantees. This PR also consolidates fragmented name generation in a
few places to use the new package.

| Old (moby/moby)                     | New                    |
|-------------------------------------|------------------------|
| namesgenerator.GetRandomName(0)     | NameWith("_")          |
| namesgenerator.GetRandomName(>0)    | NameDigitWith("_")     |
| testutil.GetRandomName(t)           | UniqueName()           |
| testutil.GetRandomNameHyphenated(t) | UniqueNameWith("-")    |

namesgenerator package API:
- NameWith(delim): random name, not unique
- NameDigitWith(delim): random name with 1-9 suffix, not unique
- UniqueName(): guaranteed unique via atomic counter
- UniqueNameWith(delim): unique with custom delimiter

Names continue to be docker style `[adjective][delim][surname]`. Unique
names are truncated to 32 characters (preserving the numeric suffix) to
fit common name length limits in Coder.

Related test flakes:
https://github.com/coder/internal/issues/1212
https://github.com/coder/internal/issues/118
https://github.com/coder/internal/issues/1068

coderd/taskname/taskname.go

@@ -12,11 +12,11 @@ import (
 
 	"github.com/anthropics/anthropic-sdk-go"
 	anthropicoption "github.com/anthropics/anthropic-sdk-go/option"
-	"github.com/moby/moby/pkg/namesgenerator"
 	"golang.org/x/xerrors"
 
 	"cdr.dev/slog/v3"
 	"github.com/coder/aisdk-go"
+	"github.com/coder/coder/v2/coderd/util/namesgenerator"
 	strutil "github.com/coder/coder/v2/coderd/util/strings"
 	"github.com/coder/coder/v2/codersdk"
 )
@@ -125,10 +125,7 @@ func generateFallback() TaskName {
 	// We have a 32 character limit for the name.
 	// We have a 5 character suffix `-ffff`.
 	// This leaves us with 27 characters for the name.
-	//
-	// `namesgenerator.GetRandomName(0)` can generate names
-	// up to 27 characters, but we truncate defensively.
-	name := strings.ReplaceAll(namesgenerator.GetRandomName(0), "_", "-")
+	name := namesgenerator.NameWith("-")
 	name = name[:min(len(name), 27)]
 	name = strings.TrimSuffix(name, "-")