fix: multi relay connectivity (#8550)

this PR, created together with @adbenitez, improves the connectivity
state passed to UI, which has changed a lot since multi relay:

- change the algorithm for `get_connectivity()`: this is roughly the
"best" connectivity of all relays now, so if one is connected, we're
already fine. this was discussed widely one to one, and that part
already closes #8554

- the PR adds a test for that, previously, that was untested

- additionally, do not regard unpublished relays in
`get_connectivity()`: e.g. unpublished relays are no longer given to
peers - so if only that is connected, the overall state should not be
"connected". therefore, we just ignore unpublished relays there

- in `get_connectivity_html()`, we continue showing unpublished relays,
however, we tune them down visually and flag them as such

- for the docs, remove the "range for some future use" wording. it was
never used like that, and that future will probably not arrive :)

<img width="320"
src="https://github.com/user-attachments/assets/1805c525-72d1-4197-b865-6e2d6fbc8819"
/>

---------

Co-authored-by: Hocuri <hocuri@gmx.de>

deltachat-ffi/deltachat.h

@@ -600,13 +600,10 @@ char*           dc_get_info                  (const dc_context_t* context);
 /**
  * Get the current connectivity, i.e. whether the device is connected to the IMAP server.
  * One of:
- * - DC_CONNECTIVITY_NOT_CONNECTED (1000-1999): Show e.g. the string "Not connected" or a red dot
- * - DC_CONNECTIVITY_CONNECTING (2000-2999): Show e.g. the string "Connecting…" or a yellow dot
- * - DC_CONNECTIVITY_WORKING (3000-3999): Show e.g. the string "Getting new messages" or a spinning wheel
- * - DC_CONNECTIVITY_CONNECTED (>=4000): Show e.g. the string "Connected" or a green dot
- *
- * We don't use exact values but ranges here so that we can split up
- * states into multiple states in the future.
+ * - DC_CONNECTIVITY_NOT_CONNECTED (1000): Show e.g. the string "Not connected" or a red dot
+ * - DC_CONNECTIVITY_CONNECTING (2000): Show e.g. the string "Connecting…" or a yellow dot
+ * - DC_CONNECTIVITY_WORKING (3000): Show e.g. the string "Getting new messages" or a spinning wheel
+ * - DC_CONNECTIVITY_CONNECTED (4000): Show e.g. the string "Connected" or a green dot
  *
  * Meant as a rough overview that can be shown 
  * e.g. in the title of the main screen.
@@ -7274,6 +7271,13 @@ void dc_event_unref(dc_event_t* event);
 /// "Message pinned by %1$s."
 #define DC_STR_MESSAGE_PINNED_BY_OTHER 244
 
+/// "Phasing out"
+///
+/// Used in connectivity view to flag unpublished relays.
+/// This should match the wording used for relay deletion confirmation,
+/// saying "Before deletion, it will be gradually phased out so your contacts can switch over smoothly"
+#define DC_STR_PHASING_OUT 245
+
 /**
  * @}
  */