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, 3 insertions, 0 deletions

diff --git a/main/cashu.h b/main/cashu.h
index 4c3d43b..76ad2eb 100644
--- a/main/cashu.h
+++ b/main/cashu.h
@@ -37,6 +37,9 @@ esp_err_t cashu_check_proof_states(const char *mint_url, const cashu_token_t *to
 uint64_t cashu_calculate_allotment_ms(uint64_t token_amount, uint64_t price_per_step,
                                        uint64_t step_size_ms);
 
+uint64_t cashu_calculate_allotment(uint64_t token_amount, uint64_t price_per_step,
+                                    const char *metric, uint64_t step_size);
+
 bool cashu_is_mint_accepted(const char *mint_url);
 
 #endif