hugofs: Make FileMeta a struct

This commit started out investigating a `concurrent map read write` issue, ending by replacing the map with a struct.

This is easier to reason about, and it's more effective:

```
name                                  old time/op    new time/op    delta
SiteNew/Regular_Deep_content_tree-16    71.5ms ± 3%    69.4ms ± 5%    ~     (p=0.200 n=4+4)

name                                  old alloc/op   new alloc/op   delta
SiteNew/Regular_Deep_content_tree-16    29.7MB ± 0%    27.9MB ± 0%  -5.82%  (p=0.029 n=4+4)

name                                  old allocs/op  new allocs/op  delta
SiteNew/Regular_Deep_content_tree-16      313k ± 0%      303k ± 0%  -3.35%  (p=0.029 n=4+4)
```

See #8749

1 files changed, 2 insertions, 2 deletions

diff --git a/resources/resource_transformers/tocss/scss/tocss.go b/resources/resource_transformers/tocss/scss/tocss.go
index f4f15fad1..de33b663e 100644
--- a/resources/resource_transformers/tocss/scss/tocss.go
+++ b/resources/resource_transformers/tocss/scss/tocss.go
@@ -55,7 +55,7 @@ func (t *toCSSTransformation) Transform(ctx *resources.ResourceTransformationCtx
 	for _, ip := range options.from.IncludePaths {
 		info, err := t.c.workFs.Stat(filepath.Clean(ip))
 		if err == nil {
-			filename := info.(hugofs.FileMetaInfo).Meta().Filename()
+			filename := info.(hugofs.FileMetaInfo).Meta().Filename
 			options.to.IncludePaths = append(options.to.IncludePaths, filename)
 		}
 	}
@@ -105,7 +105,7 @@ func (t *toCSSTransformation) Transform(ctx *resources.ResourceTransformationCtx
 			fi, err := t.c.sfs.Fs.Stat(filenameToCheck)
 			if err == nil {
 				if fim, ok := fi.(hugofs.FileMetaInfo); ok {
-					return fim.Meta().Filename(), "", true
+					return fim.Meta().Filename, "", true
 				}
 			}
 		}