Fix/issue 1629 auth emulator log spam

[AustinBenoit]

Description

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Fixed log spam and high CPU utilization when offline by moving USE_AUTH_EMULATOR environment variable check to initialization and eliminating per-request logging (#1629)

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Testing

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Locally test to make sure auth emulator can still be reached. Along with making sure no env variable still talks with prod.

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Type of Change

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• Bug fix. Add the issue # below if applicable.
• New feature. A non-breaking change which adds functionality.
• Other, such as a build process or documentation change.

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Notes

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• Read the contribution guidelines CONTRIBUTING.md.
• Changes to the public API require an internal API review. If you'd like to help us make Firebase APIs better, please propose your change in a feature request so that we can discuss it together.

Fixes Bugs:
#1629

[gemini-code-assist]

Code Review

This pull request refactors the Auth Emulator initialization on Desktop by moving the environment variable checks (USE_AUTH_EMULATOR and AUTH_EMULATOR_PORT) from per-request checks in AuthRequest to a one-time initialization in CreatePlatformAuth, addressing issues with log spam and high CPU utilization. The feedback suggests optimizing the environment variable lookup for AUTH_EMULATOR_PORT to avoid redundant calls to std::getenv and to handle empty port strings safely.