fix: guard process.memoryUsage call with typeof check for browser compatibility

[ViniciusDev26]

Fixes UnhandledRejection when logHeapUsage is true in browser environments where process is a polyfill without memoryUsage.

Description

Guard process.memoryUsage calls with a typeof check before invoking it, preventing an UnhandledRejection crash when logHeapUsage: true is set in environments where process is a polyfill without memoryUsage (e.g. browser mode).

Resolves #6500

The previous check (typeof process !== 'undefined') only verified that process existed, but not that memoryUsage was actually a
function. In browser environments, process is polyfilled but memoryUsage is not available, causing the call to throw. The fix changes
both guards in onAfterRunSuite and onAfterRunTask to typeof process?.memoryUsage === 'function'.

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[sheremet-va]

In environments that don't support memoryUsage, we wanted to use performance.measureUserAgentSpecificMemory as mentioned in the comment: #6500 (comment)