perf: Move sampling checks earlier to reduce overhead

[sohankshirsagar]

Note

Moves sampling checks to the earliest interception points for HTTP Server.prototype.emit('request') and Next.js handleRequest, removing later redundant checks.

• Instrumentation
  • HTTP:
    • Add early sampling in Server.prototype.emit('request') to short-circuit unsampled requests in RECORD mode.
    • Remove later sampling check inside _createServerSpan RECORD path.
  • Next.js:
    • Add early sampling at start of BaseServer.prototype.handleRequest to bypass unsampled requests.
    • Remove later sampling check within the RECORD branch of handleRequest.

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