Before
```console
$ go test -bench=.
goos: linux
goarch: arm64
pkg: miniflux.app/v2/internal/reader/readability
BenchmarkExtractContent-8 34 86102474 ns/op
BenchmarkGetWeight-8 10573 103045 ns/op
PASS
ok miniflux.app/v2/internal/reader/readability 5.409s
```
After
```console
$ go test -bench=.
goos: linux
goarch: arm64
pkg: miniflux.app/v2/internal/reader/readability
BenchmarkExtractContent-8 56 83130924 ns/op
BenchmarkGetWeight-8 246541 5241 ns/op
PASS
ok miniflux.app/v2/internal/reader/readability 6.026s
```
This should make ProcessFeedEntries marginally faster, while saving
some memory.
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