Fix requests timeout

[TMSCH]

Fix two issues:

• if the global timeout ends after the iframe initialization but before the resolution of an operation, it currently makes it impossible to perform the operation again because it is still pending on the provider side. To address the issue, a global request timeout triggers a cancel last operation.
• Dispose of the iframe if initialization failed to avoid clobbering the DOM.

[codecov-io]

Codecov Report

Merging #53 into master will decrease coverage by 0.15%. The diff coverage is 90.19%.

@@            Coverage Diff             @@
##           master      #53      +/-   ##
==========================================
- Coverage    91.6%   91.45%   -0.16%     
==========================================
  Files          34       34              
  Lines        1418     1451      +33     
  Branches      184      192       +8     
==========================================
+ Hits         1299     1327      +28     
- Misses        119      124       +5

Impacted Files	Coverage Δ
ts/protocol/utils.ts	81.88% <75%> (-0.43%)	:arrow_down:
ts/api/api.ts	92.07% <93.02%> (-0.58%)	:arrow_down:

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[TMSCH]

Thanks @tikurahul !