feat: expose call_intent for m.rtc.notification

[Susurrus]

This allows for notifications to use the intent for deciding how to render the message (e.g. whether to call it a "call" or a "video call"). MSC4075 specifically states these shouldn't be used for rendering in the timeline, but I'm not exactly clear why (discussion link). We'd like to use it in Fractal in lieu for now of having the membership-based call rendering, which AFAIK isn't implemented here yet. So adding this field here would be useful.

This field is also not technically in the spec (I added a comment about it), but since it's elsewhere in the SDK, figured it was fine to expose it here as well.

I left out other fields, tho there are several, as I'm not certain why these fields weren't originally exposed and didn't want to complicate things here too much.

• I've documented the public API Changes in the appropriate CHANGELOG.md files.
• This PR was made with the help of AI.

[codspeed-hq]

Merging this PR will not alter performance

✅ 50 untouched benchmarks

---

_{Comparing Susurrus:call_intent (8e2453a) with main (a65fec3)}

[codecov]

Codecov Report

❌ Patch coverage is 0% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.87%. Comparing base (a65fec3) to head (8e2453a).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
crates/matrix-sdk-ui/src/timeline/event_handler.rs	0.00%	2 Missing ⚠️
...trix-sdk-ui/src/timeline/event_item/content/mod.rs	0.00%	2 Missing ⚠️
...rates/matrix-sdk-ui/src/timeline/event_item/mod.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6412      +/-   ##
==========================================
- Coverage   89.87%   89.87%   -0.01%     
==========================================
  Files         378      378              
  Lines      103445   103446       +1     
  Branches   103445   103446       +1     
==========================================
- Hits        92973    92968       -5     
- Misses       6902     6909       +7     
+ Partials     3570     3569       -1     

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