refactor(native): Fail on empty or non-existent config environment variable

[nmahadevuni]

Description

This change is to report error when config properties reader finds an empty or non-existent envrionment variable.

Motivation and Context

If environment variable is empty or non-existent, we are quietly discarding it and loading the catalog which is causing issues while accessing the catalog assuming all is right with it.

Impact

No impact

Test Plan

Added test in ConfigTest.cpp

== NO RELEASE NOTE ==

[sourcery-ai[bot]]

Reviewer's Guide

This PR strengthens configuration handling by making the config reader fail fast when encountering empty or non-existent environment variables, and extends unit tests to verify both normal substitution behavior and the new error cases.

File-Level Changes

Change	Details	Files
Config reader now treats empty or missing environment variables as hard errors instead of silently accepting them.	Updated environment-variable extraction to check for both null and empty values returned from getenv Replaced warning log on empty env var with a VELOX_USER_FAIL throwing an error when the env var is missing or empty Kept successful substitution behavior unchanged when a valid non-empty env var is present	presto-native-execution/presto_cpp/main/common/ConfigReader.cpp
ReadConfig environment variable tests expanded to cover invalid env var scenarios and verify error behavior.	Stopped setting the previously-used empty environment variable in the happy-path test setup and removed it from the expected properties map Introduced a reusable helper lambda to write a config file and assert that readConfig throws with a specific error message Added tests to validate that readConfig throws when an environment variable is configured but empty, and when it is configured but not defined in the environment Introduced a constant for a non-existent environment variable name to drive the failure-path test	presto-native-execution/presto_cpp/main/common/tests/ConfigTest.cpp

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