contrib: Fixup verify-binaries OS platform parsing

Parse platform strings with "-" or '.' correctly such as "linux-gnu" or
"x86_64-linux-gnu.tar.gz" to download the matching files or file. String
partition() is used to tolerate more dashes. Update `VERSION_EXAMPLE`
with a new string parsed correctly now. Fix "-aarch64" interpreted as a
release candidate due to sub-string "rc", causing all downloads to fail.
Now "rc" must immediately follow first "-" to indicate an [-rc] string.
Local variables `version_rc`, `version_os` renamed to `rc`, `platform`.
If "-rcN" is specified, `platform` is reassigned to remove the '-rcN'.

Changes are useful to only download one bitcoin core binary on slow
connections. Making `verify.py pub` more intuitive, robust, and
versatile. Closes #30145

When user types a platform string not found in any filename lets help
and say the platform closest to what they typed in a `f"No files
matched the platform specified. Did you mean: {closest_match}"` log.
Improves UX when unaware how we name our files.
Uses the difflib Python built-in which was already imported elsewhere.

Update test.py to test single file verification
verify-binaries/verify.py can accept an entire filename filter for its
"-platform" parameter now so let us test that it succeeds and downloads
and verifies only one file. `verify.py pub 22.0-x86_64-linux-gnu.tar.gz`
should get and verify only the requested binary. It is placed before the
existing <version> wide verification as it is a faster test and possibly
easier to break.

Update doc with examples now possible after bugfix
Add example to show release candidates now work with "-platform" strings
containing "-" and string provided can be from the middle of filename:
`./contrib/verify-binaries/verify.py --json pub 23.0-rc5-linux-gnu`
Change example 5 to not match example 3.
New examples to show platform can now be provided specifically enough to
download only a single binary down to its file extension:
`./contrib/verify-binaries/verify.py pub 25.2-x86_64-linux`
`./contrib/verify-binaries/verify.py pub 24.1-rc1-darwin`
`./contrib/verify-binaries/verify.py pub 27.0-win64-setup.exe`
This is the most common use if not verifying all files so users see it
as the first example for "only download the binaries for a certain
architecture and/or platform". Downloading one file is intuitively what
most will think this meant and this change delivers on that expectation.

Co-authored-by: stickies-v

contrib/verify-binaries/README.md

@@ -50,6 +50,7 @@ Get JSON output and don't prompt for user input (no auto key import):
 
 ```sh
 ./contrib/verify-binaries/verify.py --json pub 22.0-x86
+./contrib/verify-binaries/verify.py --json pub 23.0-rc5-linux-gnu
 ```
 
 Rely only on local GPG state and manually specified keys, while requiring a
@@ -57,14 +58,15 @@ threshold of at least 10 trusted signatures:
 ```sh
 ./contrib/verify-binaries/verify.py \
     --trusted-keys 74E2DEF5D77260B98BC19438099BAD163C70FBFA,9D3CC86A72F8494342EA5FD10A41BDC3F4FAFF1C \
-    --min-good-sigs 10 pub 22.0-x86
+    --min-good-sigs 10 pub 22.0-linux
 ```
 
-If you only want to download the binaries for a certain platform, add the corresponding suffix, e.g.:
+If you only want to download the binaries for a certain architecture and/or platform, add the corresponding suffix, e.g.:
 
 ```sh
-./contrib/verify-binaries/verify.py pub 24.0.1-darwin
-./contrib/verify-binaries/verify.py pub 23.1-rc1-win64
+./contrib/verify-binaries/verify.py pub 25.2-x86_64-linux
+./contrib/verify-binaries/verify.py pub 24.1-rc1-darwin
+./contrib/verify-binaries/verify.py pub 27.0-win64-setup.exe
 ```
 
 If you do not want to keep the downloaded binaries, specify the cleanup option.