Use streaming when downloading from DOI

[koppor]

Fixes #14089

Was a bit larger than I thought; the DoiFetcher code needed a cleanup. There was also a space inserted. I don't know why this disappeared when reading from the String; maybe there was some automatic trimming. I added DoiFetcher.http for easy manual checking of the returned file.

Steps to test

Just see the fetcher tests passing.

Mandatory checks

• I own the copyright of the code submitted and I license it under the MIT license
• [/] I manually tested my changes in running JabRef (always required)
• I added JUnit tests for changes (if applicable)
• [/] I added screenshots in the PR description (if change is visible to the user)
• [/] I described the change in CHANGELOG.md in a way that is understandable for the average user (if change is visible to the user)
• [/] I checked the user documentation: Is the information available and up to date? If not, I created an issue at https://github.com/JabRef/user-documentation/issues or, even better, I submitted a pull request updating file(s) in https://github.com/JabRef/user-documentation/tree/main/en.

[koppor]

Format fails because formatter does not work with Markdown properly (yet). EAP does.

--- a/jablib/src/main/java/org/jabref/logic/net/URLDownload.java
+++ b/jablib/src/main/java/org/jabref/logic/net/URLDownload.java
@@ -61,7 +61,7 @@ import org.slf4j.LoggerFactory;
 /// String content = dl.asString(ENCODING);
 /// dl.toFile(Path);              // available in FILE
 /// String contentType = dl.getMimeType();
-/// ```
+///```
 ///
 /// Almost every call to a public method creates a new HTTP connection
 /// (except for {@link #asString(Charset, URLConnection) asString},

I filed https://github.com/leventeBajczi/intellij-idea-format/pull/4/files to check whether the latest version works.

[Siedlerchr]

Count and page numbers are two different thing
E.g total pages

[Siedlerchr]

Add tests

[Siedlerchr]

Add a test