[ayushmishra2005]

Closes #1706

Intent

Improve the readability of SharedPool's trailing storage representation and simplify pool initialization without changing behavior.

Implementation

• Replaced the trailing marker field

  void align(@alignOf(Node))

  with

  [0]Node

which preserves layout while more clearly expressing the flexible-array pattern.

• Simplified buf() and constBuf() by removing unnecessary pointer casts.
• Added initInBuffer, allowing callers to initialize a pool directly from an aligned byte buffer while validating the required size.
• Updated replay service call sites to use the new helper.
• Added tests covering:
  • layout assumptions
  • initialization from a buffer
  • allocation, exhaustion, free, and reuse