Fix infinite recursion when a @Suggestions method returns a CompletableFuture

[emilyy-dev]

MethodSuggestionProvider#mapSuggestions calls itself when the method's input (the @Suggestions method return value) is a CompletableFuture, instead of the unused #mapFuture, leading to a StackOverflowError.

[github-actions]

Test Results

 88 files  ±0   88 suites  ±0   10s ⏱️ -4s
429 tests +1  429 ✅ +1  0 💤 ±0  0 ❌ ±0 
474 runs  +1  474 ✅ +1  0 💤 ±0  0 ❌ ±0 

Results for commit c9e7dd4. ± Comparison against base commit 8c3d2e6.

This pull request removes 3 and adds 4 tests. Note that renamed tests count towards both.

org.incendo.cloud.annotations.feature.MethodSuggestionProviderTest ‑ [5] instance=string list source
org.incendo.cloud.annotations.feature.MethodSuggestionProviderTest ‑ [6] instance=source with CommandInput injected
org.incendo.cloud.annotations.feature.MethodSuggestionProviderTest ‑ [7] instance=source with injected value

org.incendo.cloud.annotations.feature.MethodSuggestionProviderTest ‑ [5] instance=list future source
org.incendo.cloud.annotations.feature.MethodSuggestionProviderTest ‑ [6] instance=string list source
org.incendo.cloud.annotations.feature.MethodSuggestionProviderTest ‑ [7] instance=source with CommandInput injected
org.incendo.cloud.annotations.feature.MethodSuggestionProviderTest ‑ [8] instance=source with injected value

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