Repace the `Memo` struct with `ReadSignal`

[lukechu10]

Memo used to be a wrapper struct around ReadSignal which did not provide anything extra so this makes everything simpler.

Follow-up to #626

[github-actions[bot]]

Benchmark Report

• wasm-bindgen: the performance goal
• baseline: performance of sycamore-baseline (typically latest master)
• update: performance of sycamore (typically recent changes)
• diff: measures the improvement of update over the baseline

  
  @@                           Performance Diff                           @@

| wasm-bindgen | baseline | update | diff

########################################################################## 01_run1k | 10.68 | 21.79 | 22.08 | +1.32% 02_replace1k | 16.80 | 34.73 | 34.24 | -1.40%

• 03_update10th1k_x16 | 8.61 | 14.57 | 13.52 | -7.19%
• 04_select1k | 1.89 | 22.36 | 16.49 | -26.24%
• 05_swap1k | 0.69 | 2.23 | 2.00 | -10.32%
• 06_remove-one-1k | 0.67 | 3.06 | 2.60 | -14.90% 07_create10k | 100.57 | 245.91 | 250.82 | +2.00% 08_create1k-after1k_x2 | 20.38 | 45.15 | 46.11 | +2.12% 09_clear1k_x8 | 52.11 | 69.34 | 68.61 | -1.05% 21_ready-memory | 1.71 | 1.75 | 1.75 | -0.01% 22_run-memory | 2.97 | 4.85 | 4.85 | +0.02% 23_update5-memory | 2.91 | 4.96 | 4.96 | -0.00% 25_run-clear-memory | 1.81 | 3.52 | 3.52 | -0.00% 26_run-10k-memory | 14.91 | 41.18 | 41.18 | +0.00% 31_startup-ci | 1918.82 | 2264.32 | 2251.35 | -0.57% 32_startup-bt | 28.52 | 82.82 | 81.02 | -2.17% 33_startup-mainthreadcost | 294.52 | 357.57 | 356.56 | -0.28% 34_startup-totalbytes | 185.58 | 299.40 | 299.23 | -0.06%

  
  Workflow: [6434239255](/sycamore-rs/sycamore/actions/runs/6434239255)
  *Adding new commits will generate a new report*