Add new logger

src/logger/README.md

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+# Logger
+
+Simple logger for Bluesky. Supports log levels, debug contexts, and separate
+transports for production, dev, and test mode.
+
+## At a Glance
+
+```typescript
+import { logger } from '#/logger'
+
+logger.debug(message[, metadata, debugContext])
+logger.info(message[, metadata])
+logger.log(message[, metadata])
+logger.warn(message[, metadata])
+logger.error(error[, metadata])
+```
+
+#### Modes
+
+The "modes" referred to here are inferred from the values exported from `#/env`.
+Basically, the booleans `IS_DEV`, `IS_TEST`, and `IS_PROD`.
+
+#### Log Levels
+
+Log levels are used to filter which logs are either printed to the console
+and/or sent to Sentry and other reporting services. To configure, set the
+`EXPO_PUBLIC_LOG_LEVEL` environment variable in `.env` to one of `debug`,
+`info`, `log`, `warn`, or `error`.
+
+This variable should be `info` in production, and `debug` in dev. If it gets too
+noisy in dev, simply set it to a higher level, such as `warn`.
+
+## Usage
+
+```typescript
+import { logger } from '#/logger';
+```
+
+### `logger.error`
+
+The `error` level is for... well, errors. These are sent to Sentry in production mode.
+
+`error`, along with all log levels, supports an additional parameter, `metadata: Record<string, unknown>`. Use this to provide values to the [Sentry
+breadcrumb](https://docs.sentry.io/platforms/react-native/enriching-events/breadcrumbs/#manual-breadcrumbs).
+
+```typescript
+try {
+  // some async code
+} catch (e) {
+  logger.error(e, { ...metadata });
+}
+```
+
+### `logger.warn`
+
+Warnings will be sent to Sentry as a separate Issue with level `warning`, as
+well as as breadcrumbs, with a severity level of `warning`
+
+### `logger.log`
+
+Logs with level `log` will be sent to Sentry as a separate Issue with level `log`, as
+well as as breadcrumbs, with a severity level of `default`.
+
+### `logger.info`
+
+The `info` level should be used for information that would be helpful in a
+tracing context, like Sentry. In production mode, `info` logs are sent
+to Sentry as breadcrumbs, which decorate log levels above `info` such as `log`,
+`warn`, and `error`.
+
+### `logger.debug`
+
+Debug level is really only intended for local development. Use this instead of
+`console.log`.
+
+```typescript
+logger.debug(message, { ...metadata });
+```
+
+Inspired by [debug](https://www.npmjs.com/package/debug), when writing debug
+logs, you can optionally pass a _context_, which can be then filtered when in
+debug mode.
+
+This value should be related to the feature, component, or screen
+the code is running within, and **it should be defined in `#/logger/debugContext`**.
+This way we know if a relevant context already exists, and we can trace all
+active contexts in use in our app. This const enum is conveniently available on
+the `logger` at `logger.DebugContext`.
+
+For example, a debug log like this:
+
+```typescript
+logger.debug(message, {}, logger.DebugContext.composer);
+```
+
+Would be logged to the console in dev mode if `EXPO_PUBLIC_LOG_LEVEL=debug`, _or_ if you
+pass a separate environment variable `LOG_DEBUG=composer`. This variable supports
+multiple contexts using commas like `LOG_DEBUG=composer,profile`, and _automatically
+sets the log level to `debug`, regardless of `EXPO_PUBLIC_LOG_LEVEL`._