Photo: one async method per EXIF field (closes #148)

`Photo` gains thirteen async methods, one per `PhotoExif` field and named after it: `make()`, `model()`, `lensModel()`, `dateTimeOriginal()`, `offsetTimeOriginal()`, `exposureTime()`, `fNumber()`, `iso()`, `focalLength()`, `orientation()`, `gpsLatitude()`, `gpsLongitude()` and `gpsAltitude()`. Each calls `exif()` and returns its one field, or `undefined` when the file lacks it. `exif()` is unchanged.

`Photo` implements a type built from `PhotoExif`'s keys, so the type check fails when a field has no method. Each call reads the original again; a caller that wants several fields calls `exif()` once.

Model: opus-5-5

README.md

@@ -726,7 +726,7 @@ synchronous getters look at the disk and never touch the network:
 - `photo.isLocal` → `boolean` — whether the whole original is at `savePath`. A
   copy only in the cache does not count.
 
-Five async methods may download:
+These async methods may download:
 
 - `await photo.original(opts?)` → `{ path, bytes, videoPath? }` — the
   full-resolution file. For a live photo, `path` and `bytes` are its image's and
@@ -748,6 +748,12 @@ Five async methods may download:
   UTC. EXIF is read from any image format exifreader reads (such as JPEG,
   HEIC/HEIF, AVIF, PNG, WebP and TIFF), a live photo's image included. Any other
   original gives `{}`, and a video gives `{}` without being downloaded.
+- `await photo.make(opts?)`, and likewise `model()`, `lensModel()`,
+  `dateTimeOriginal()`, `offsetTimeOriginal()`, `exposureTime()`, `fNumber()`,
+  `iso()`, `focalLength()`, `orientation()`, `gpsLatitude()`, `gpsLongitude()`
+  and `gpsAltitude()` → one field of `exif()` each, typed as in `PhotoExif`, or
+  `undefined` when the file lacks it. Each calls `exif()` with its `opts`, so
+  each call reads the original again.
 
 They serve from the on-disk content cache when the bytes are present and
 otherwise fetch through the pools; `original()`, `content()` and `exif()` also