[MedChronicle]

Add extension helpers: typed getters, string decoding, counting/iteration, depth, minify and prettify

Description

Adds a new optional extension module (core_json_ext.c / core_json_ext.h) on top of the public coreJSON API. core_json.c and core_json.h are not modified. The module uses only JSON_Validate, JSON_SearchConst and JSON_Iterate, and never allocates memory (the caller supplies all output buffers).

New functions:

• JSON_GetInt, JSON_GetDouble, JSON_GetBool: typed getters with type and overflow checks (LLONG_MIN handled correctly).
• JSON_GetString: decodes escapes (\n, \", \uXXXX including surrogate pairs) to UTF-8 and NUL-terminates. Rejects \u0000.
• JSON_Exists, JSON_GetType: check whether a key exists and what type it is.
• JSON_Count, JSON_ForEach: count elements or iterate an object/array with a callback (early stop supported).
• JSON_GetDepth: maximum nesting depth of a document.
• JSON_Minify, JSON_Prettify: compact or pretty-print into a caller buffer. *outLength always reports the required size, so callers can resize on JSONBadParameter.
• JSON_StatusToString, JSON_TypeToString: readable names for status and type codes.

Build change: core_json_ext.c is added to JSON_SOURCES in jsonFilePaths.cmake. Linking requires -lm (strtod, isinf).

Also adds examples/demo.c (usage example) and examples/test_ext.c (ad-hoc test program).

Test Steps

1. Build and run the test program with strict warnings and sanitizers:
   gcc -std=c99 -Wall -Wextra -Wpedantic -g -fsanitize=address,undefined -Isource/include source/core_json.c source/core_json_ext.c examples/test_ext.c -o test_ext -lm && ./test_ext
2. Expected output ends with ALL TESTS PASSED.
3. Build and run the demo:
   gcc -std=c99 -Wall -Wextra -Isource/include source/core_json.c source/core_json_ext.c examples/demo.c -o demo -lm && ./demo
4. Expected output includes name = Sarthak, age = 20, tags = 3 items, missing -> JSONNotFound, followed by the pretty-printed JSON.

Checklist:

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

Related Issue

None.

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