fix: Check plan outcome when calling Plan objects

[tpoliaw]

When using the client.plans.plan_name() approach to running plans, the
task status returned by the server was not being checked so that plans
failing did not raise exceptions on the client side.

Checking the task status also allows values returned by plans to be
accessed easily if they were serializable.

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 95.08%. Comparing base (57ed429) to head (654e59b).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
src/blueapi/client/client.py	66.66%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1470      +/-   ##
==========================================
- Coverage   95.20%   95.08%   -0.12%     
==========================================
  Files          43       43              
  Lines        3128     3136       +8     
==========================================
+ Hits         2978     2982       +4     
- Misses        150      154       +4     

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