Add totalTokens field to Usage type

- Added totalTokens field to Usage interface in pi-ai
- Anthropic: computed as input + output + cacheRead + cacheWrite
- OpenAI/Google: uses native total_tokens/totalTokenCount
- Fixed openai-completions to compute totalTokens when reasoning tokens present
- Updated calculateContextTokens() to use totalTokens field
- Added comprehensive test covering 13 providers

fixes #130

packages/ai/test/handoff.test.ts

@@ -46,6 +46,7 @@ const providerContexts = {
 				output: 50,
 				cacheRead: 0,
 				cacheWrite: 0,
+				totalTokens: 150,
 				cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 },
 			},
 			stopReason: "toolUse",
@@ -97,6 +98,7 @@ const providerContexts = {
 				output: 60,
 				cacheRead: 0,
 				cacheWrite: 0,
+				totalTokens: 180,
 				cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 },
 			},
 			stopReason: "toolUse",
@@ -147,6 +149,7 @@ const providerContexts = {
 				output: 55,
 				cacheRead: 0,
 				cacheWrite: 0,
+				totalTokens: 165,
 				cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 },
 			},
 			stopReason: "toolUse",
@@ -199,6 +202,7 @@ const providerContexts = {
 				output: 58,
 				cacheRead: 0,
 				cacheWrite: 0,
+				totalTokens: 173,
 				cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 },
 			},
 			stopReason: "toolUse",
@@ -243,6 +247,7 @@ const providerContexts = {
 				output: 25,
 				cacheRead: 0,
 				cacheWrite: 0,
+				totalTokens: 75,
 				cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 },
 			},
 			stopReason: "error",