Add codecov operation and reduce warning threshold to 40% in build.py

[Copilot]

Updates build configuration to enable code coverage collection and reduce the minimum coverage warning threshold from 70% to 40% across all targets.

Changes

• Added codecov operation to all three targets (iOS Library, Mac Library, Vision Library)
• Reduced min_warn_codecov from 70.0 to 40.0 for all targets

target_specifiers = [
    {
        "name" : "iOS Library",
        "target" : "ios_library",
        "scheme" : "IdentityCore iOS",
-       "operations" : [ "build", "test" ],
+       "operations" : [ "build", "test", "codecov" ],
-       "min_warn_codecov" : 70.0,
+       "min_warn_codecov" : 40.0,
        "platform" : "iOS",
    },
    # Similar updates for Mac Library and Vision Library targets
]

The codecov operation triggers code coverage collection during builds (via -enableCodeCoverage YES flag) and generates coverage reports using llvm-cov.

Original prompt

On build.py, In this file, update the operations in all targets to include operation for code coverage. Also reduce the minimum codecov warning threshold to 40 instead of 70 in all targets

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[azure-pipelines]

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