Constify the init secret length

Unexport it since this is internal.

Author: fgsch

internal/abi/fastly/hostcalls_guest.go

@@ -2268,7 +2268,7 @@ func (s *Secret) Plaintext() ([]byte, error) {
 	// Most secrets will fit into the initial secret buffer size, so
 	// we'll start with that. If it doesn't fit, we'll know the exact
 	// size of the buffer to try again.
-	buf := prim.NewWriteBuffer(InitialSecretLen)
+	buf := prim.NewWriteBuffer(initialSecretLen)
 
 	status := fastlySecretPlaintext(
 		s.h,

internal/abi/fastly/types.go

@@ -278,9 +278,6 @@ const (
 	cacheOverrideTagPCI                  cacheOverrideTag = 0b0000_1000 // $pci
 )
 
-// InitialSecretLen is the initial size of the buffer to use for decrypting secrets
-var InitialSecretLen = 1024
-
 const (
 	// DefaultMaxHeaderNameLen is the default header name length limit
 	DefaultMaxHeaderNameLen = 8192
@@ -293,6 +290,8 @@ const (
 
 	dictionaryValueMaxLen = 8192 // https://docs.fastly.com/en/guides/about-edge-dictionaries#limitations-and-considerations
 	defaultBufferLen      = 16 * 1024
+
+	initialSecretLen = 1024
 )
 
 // CacheOverrideOptions collects specific, caching-related options for outbound