test: centralize fetch mocks in one place

[nolanlawson]

This is just a refactor of the fetch mocking in the test code so that it's easier to set a universal delay.

It also includes a code comment about an apparent race condition, see #407.

[github-actions[bot]]

📊 Tachometer Benchmark Results

Summary

benchmark-total

• emoji-picker-element-change-tab: unsure 🔍 -1% - +1% (-0.45ms - +0.31ms)
  ^{this-change vs tip-of-tree}
• emoji-picker-element-database-interactions: unsure 🔍 -3% - +3% (-2.64ms - +3.05ms)
  ^{this-change vs tip-of-tree}
• emoji-picker-element-first-load: unsure 🔍 -4% - +4% (-2.20ms - +2.38ms)
  ^{this-change vs tip-of-tree}
• emoji-picker-element-search: unsure 🔍 -0% - +0% (-0.10ms - +0.04ms)
  ^{this-change vs tip-of-tree}
• emoji-picker-element-second-load: unsure 🔍 -6% - +6% (-2.20ms - +2.14ms)
  ^{this-change vs tip-of-tree}

Results

emoji-picker-element-change-tab

• Browser: chrome-headless 122.0.6261.94
• Sample size: 50
• Built by: Benchmarks #388
• Commit: 79599bf

Version	Avg time	vs this-change	vs tip-of-tree tip-of-tree
this-change	33.36ms - 33.72ms	-	unsure 🔍 -1% - +1% -0.45ms - +0.31ms
tip-of-tree tip-of-tree	33.28ms - 33.95ms	unsure 🔍 -1% - +1% -0.31ms - +0.45ms	-

emoji-picker-element-database-interactions

• Browser: chrome-headless 122.0.6261.94
• Sample size: 50
• Built by: Benchmarks #388
• Commit: 79599bf

Version	Avg time	vs this-change	vs tip-of-tree tip-of-tree
this-change	95.13ms - 99.28ms	-	unsure 🔍 -3% - +3% -2.64ms - +3.05ms
tip-of-tree tip-of-tree	95.06ms - 98.95ms	unsure 🔍 -3% - +3% -3.05ms - +2.64ms	-

emoji-picker-element-first-load

• Browser: chrome-headless 122.0.6261.94
• Sample size: 50
• Built by: Benchmarks #388
• Commit: 79599bf

Version	Avg time	vs this-change	vs tip-of-tree tip-of-tree
this-change	53.21ms - 56.22ms	-	unsure 🔍 -4% - +4% -2.20ms - +2.38ms
tip-of-tree tip-of-tree	52.90ms - 56.35ms	unsure 🔍 -4% - +4% -2.38ms - +2.20ms	-

emoji-picker-element-search

• Browser: chrome-headless 122.0.6261.94
• Sample size: 50
• Built by: Benchmarks #388
• Commit: 79599bf

Version	Avg time	vs this-change	vs tip-of-tree tip-of-tree
this-change	49.97ms - 50.09ms	-	unsure 🔍 -0% - +0% -0.10ms - +0.04ms
tip-of-tree tip-of-tree	50.02ms - 50.10ms	unsure 🔍 -0% - +0% -0.04ms - +0.10ms	-

emoji-picker-element-second-load

• Browser: chrome-headless 122.0.6261.94
• Sample size: 50
• Built by: Benchmarks #388
• Commit: 79599bf

Version	Avg time	vs this-change	vs tip-of-tree tip-of-tree
this-change	37.19ms - 40.38ms	-	unsure 🔍 -6% - +6% -2.20ms - +2.14ms
tip-of-tree tip-of-tree	37.35ms - 40.28ms	unsure 🔍 -6% - +6% -2.14ms - +2.20ms	-

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[github-actions[bot]]

Size Change: 0 B

Total Size: 36.6 kB

ℹ️ View Unchanged

| Filename | Size | | :--- | :---: | | `./bundle.js` | 36.6 kB |

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