fix: reset StartupLogger on JS reload so runJsBundleStart marker is recorded

[mohanrajvenkatesan2304-hash]

Summary:

This is a regression in 0.83 from PR #54255, which made StartupLogger reset itself when APP_STARTUP_START fires. On JS reload, RUN_JS_BUNDLE_START and INIT_REACT_RUNTIME_START arrive first and are rejected as duplicates by the still-populated logger; only afterward does APP_STARTUP_START fire and clear the state. The result is NaN start times paired with valid end times, so performance.measure('runJsBundle', 'runJsBundleStart', 'runJsBundleEnd') throws The mark 'runJsBundleStart' does not exist. on every reload after the first load.

The fix is to pre-emptively call StartupLogger::reset() at the top of ReactInstance::loadScript so every load (including reloads) starts with a clean logger and the startup markers are recorded correctly each time.

Fixes #56339.

Changelog:

[GENERAL] [FIXED] - Reset StartupLogger on JS reload so runJsBundleStart performance marker is recorded after the first load

Test Plan:

• Manual: ran the reporter's reproducer (linked from runJsBundleStart performance marker dropped on JS reload due to APP_STARTUP_START reset cascade in ReactInstance::loadScript (regression in 0.83) #56339): app boots, performance.measure('runJsBundle', 'runJsBundleStart', 'runJsBundleEnd') succeeds; press R to reload, measure succeeds again instead of throwing The mark 'runJsBundleStart' does not exist.
• clang-format -i packages/react-native/ReactCommon/react/runtime/ReactInstance.cpp — no diff
• yarn lint / format-check / flow-check / test: not applicable (touched file is C++; eslint/prettier/flow scopes are JS only). Could not run these in the dev sandbox due to no outbound network for yarn install; see commit for the C++-only nature of the change.

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@fabriziocucci has imported this pull request. If you are a Meta employee, you can view this in D102561906.