Add unit coverage for core and bare-metal HALs

[DemonGiggle]

Summary

• add unit tests for JSON writer/parser behavior and session message history/view semantics
• add bare-metal HAL tests for UART line handling, truncation warnings, socket delegation, and single-socket lifecycle
• include the new unit and bare-metal HAL tests in POSIX and host-sim CI jobs

Verification

• cmake -S . -B build-posix -DEC_PLATFORM=POSIX -DEC_ENABLE_TLS=OFF
• cmake --build build-posix
• ctest --test-dir build-posix --output-on-failure
• cmake -S . -B build-host-sim -DEC_PLATFORM=POSIX -DEC_HOST_SIM=ON -DEC_ENABLE_TLS=OFF
• cmake --build build-host-sim
• ctest --test-dir build-host-sim --output-on-failure
• cmake -S . -B build-baremetal -DEC_PLATFORM=BAREMETAL -DEC_ENABLE_TLS=OFF
• cmake --build build-baremetal
• cmake -S . -B build-baremetal-tls -DEC_PLATFORM=BAREMETAL -DEC_ENABLE_TLS=ON
• cmake --build build-baremetal-tls

[gemini-code-assist]

Code Review

This pull request introduces a comprehensive testing suite, including unit tests for JSON processing and session management, as well as HAL-level tests for bare-metal UART and socket implementations. The review feedback highlights several opportunities to improve test robustness, specifically by clearing global HAL pointers at the end of tests to prevent dangling references and addressing a potential buffer overflow during socket data reception.

[gemini-code-assist]

The UART HAL and context pointers are stored in global variables (s_uart_hal and s_uart_ctx) but point to local stack variables within this test. To prevent dangling pointers that could cause issues if more tests are added or reordered, these globals should be cleared before the function returns.

    ec_io_uart_set_hal(NULL);
    s_uart_ctx = NULL;
    return 1;

[gemini-code-assist]

Similar to the previous test, the global HAL and context pointers should be cleared to avoid leaving the test suite in an inconsistent state with dangling pointers.

    ec_io_uart_set_hal(NULL);
    s_uart_ctx = NULL;
    return 1;

[gemini-code-assist]

Potential buffer overflow: if ec_socket_recv returns the full size of the buffer (32), the subsequent null-termination buf[n] = '\0' will write one byte past the end of the array. You should pass sizeof(buf) - 1 to the receive function to ensure space for the terminator.

Suggested change

	int n = ec_socket_recv(sock, buf, sizeof(buf), 100);
	ASSERT(n > 0, "recv should delegate to HAL");
	buf[n] = '\0';
	int n = ec_socket_recv(sock, buf, sizeof(buf) - 1, 100);
	ASSERT(n > 0, "recv should delegate to HAL");
	buf[n] = '\0';

[gemini-code-assist]

The socket HAL pointer should be cleared before the test returns to prevent other tests from accidentally using a dangling pointer to this function's stack.

    ec_socket_baremetal_set_hal(NULL);
    return 1;