Parsing CREG/CGREG/CEREG separately.

[ActoryOu]

Parsing CREG/CGREG/CEREG separately.

Description

Like FreeRTOS forum post mentioned, the cellular interface doesn't handle CGREG RAC correctly. To parse all these reg status better, this PR separates the parsing flow into different functions.

• Separate register status parsing for CREG/CGREG/CEREG.
• Early break if any parsing error happens.
• Adjust UT cases with the change.

Test Steps

1. UT
   1. Create UT new test cases
   2. Execute UT
   3. Achieve 100% coverage
2. Real target test from forum customer.
   • https://forums.freertos.org/t/cellular-interface-cgreg-parsing/21837/4

Checklist:

• [x] I have tested my changes. No regression in existing tests.
• [x] I have modified and/or added unit-tests to cover the code changes in this Pull Request.

Related Issue

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