feat(phase6): bytes-based billing - dual metric support

- session_create_bytes() + session_add_bytes() for bytes-metric sessions
- session_is_expired() dispatches on config metric (bytes vs milliseconds)
- cashu_calculate_allotment() unified dispatcher for both metrics
- tollgate_api discovery/usage/session_event use configured metric
- config: metric field defaults to 'bytes', step_size_bytes=22020096 (21MB)
- 14 new unit tests (148 total passing)
- ASSERT_EQ_UINT64 macro added to test framework

1 files changed, 7 insertions, 0 deletions

diff --git a/main/session.h b/main/session.h
index 8e2d48d..6282f5a 100644
--- a/main/session.h
+++ b/main/session.h
@@ -13,6 +13,8 @@ typedef struct {
     char mac[SESSION_MAX_MAC_LEN];
     uint64_t allotment_ms;
     int64_t start_time_ms;
+    uint64_t allotment_bytes;
+    uint64_t bytes_consumed;
     bool active;
     char spent_secrets[5][65];
     int spent_secret_count;
@@ -23,6 +25,11 @@ esp_err_t session_manager_init(void);
 session_t *session_create(uint32_t client_ip, uint64_t allotment_ms,
                           const char *spent_secrets[], int secret_count);
 
+session_t *session_create_bytes(uint32_t client_ip, uint64_t allotment_bytes,
+                                const char *spent_secrets[], int secret_count);
+
+void session_add_bytes(uint32_t client_ip, uint64_t bytes);
+
 session_t *session_find_by_ip(uint32_t client_ip);
 session_t *session_find_by_mac(const char *mac);