Observability CBOR encoding (buffer sizing)

Topics
	CBOR encoding (no mutex)
	Encodes an observability snapshot to CBOR without acquiring any mutex.

Files
file	nrf_edgeai_obsv_encode_sizes.h

Macros
#define	NRF_EDGEAI_OBSV_ENCODE_METRIC_SIZE(n_rows, n_cols)
	CBOR encoded size budget for one custom metric.
#define	NRF_EDGEAI_OBSV_ENCODE_MAX_SIZE
	Largest encoded observability CBOR payload (bytes) for one context.
#define	NRF_EDGEAI_OBSV_ENCODE_LIST_BUF_SIZE(n)
	Buffer size (bytes) required for an obsv-list encoding of n contexts.

Detailed Description