feat: start logging token usage and subscriptions (#2)

### Explanation

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### Issue

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### Attestations

- [x] I have read and agree to the [Code of Conduct](https://docs.nhcarrigan.com/community/coc/)
- [x] I have read and agree to the [Community Guidelines](https://docs.nhcarrigan.com/community/guide/).
- [x] My contribution complies with the [Contributor Covenant](https://docs.nhcarrigan.com/dev/covenant/).

### Dependencies

- [x] I have pinned the dependencies to a specific patch version.

### Style

- [x] I have run the linter and resolved any errors.
- [x] My pull request uses an appropriate title, matching the conventional commit standards.
- [x] My scope of feat/fix/chore/etc. correctly matches the nature of changes in my pull request.

### Tests

- [ ] My contribution adds new code, and I have added tests to cover it.
- [ ] My contribution modifies existing code, and I have updated the tests to reflect these changes.
- [x] All new and existing tests pass locally with my changes.
- [x] Code coverage remains at or above the configured threshold.

### Documentation

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### Versioning

Minor - My pull request introduces a new non-breaking feature.

Reviewed-on: nhcarrigan/cordelia-taryne#2
Co-authored-by: Naomi Carrigan <commits@nhcarrigan.com>
Co-committed-by: Naomi Carrigan <commits@nhcarrigan.com>

src/utils/calculateCost.ts

@@ -0,0 +1,30 @@
+/**
+ * @copyright nhcarrigan
+ * @license Naomi's Public License
+ * @author Naomi Carrigan
+ */
+import { logger } from "./logger.js";
+import type { Usage } from "@anthropic-ai/sdk/resources/index.js";
+
+/**
+ * Calculates the cost of a command run by a user, and sends to
+ * our logging service.
+ * @param usage -- The usage payload from Anthropic.
+ * @param uuid -- The Discord ID of the user who ran the command.
+ * @param command -- The command that was run.
+ */
+export const calculateCost = async(
+  usage: Usage,
+  uuid: string,
+  command: string,
+): Promise<void> => {
+  const inputCost = usage.input_tokens * (3 / 1_000_000);
+  const outputCost = usage.output_tokens * (15 / 1_000_000);
+  const totalCost = inputCost + outputCost;
+  await logger.log(
+    "info",
+    `User ${uuid} ran \`${command}\` which accepted ${usage.input_tokens.toString()} and generated ${usage.output_tokens.toString()}.
+    
+    Total cost: ${totalCost.toLocaleString("en-GB", { currency: "USD", style: "currency" })}`,
+  );
+};

src/utils/logHandler.ts

@@ -1,31 +0,0 @@
-/**
- * @copyright nhcarrigan
- * @license Naomi's Public License
- * @author Naomi Carrigan
- */
-import { createLogger, format, transports, config } from "winston";
-
-const { combine, timestamp, colorize, printf } = format;
-
-/**
- * Standard log handler, using winston to wrap and format
- * messages. Call with `logHandler.log(level, message)`.
- * @param {string} level - The log level to use.
- * @param {string} message - The message to log.
- */
-export const logHandler = createLogger({
-  exitOnError: false,
-  format:      combine(
-    timestamp({
-      format: "YYYY-MM-DD HH:mm:ss",
-    }),
-    colorize(),
-    printf((info) => {
-      // eslint-disable-next-line @typescript-eslint/restrict-template-expressions -- Winston properties...
-      return `${info.level}: ${info.timestamp}: ${info.message}`;
-    }),
-  ),
-  level:      "silly",
-  levels:     config.npm.levels,
-  transports: [ new transports.Console() ],
-});

src/utils/logger.ts

@@ -0,0 +1,12 @@
+/**
+ * @copyright nhcarrigan
+ * @license Naomi's Public License
+ * @author Naomi Carrigan
+ */
+
+import { Logger } from "@nhcarrigan/logger";
+
+export const logger = new Logger(
+  "Cordelia Taryne",
+  process.env.LOG_TOKEN ?? "",
+);