📝 Add async logger write API docs

docs/api/async-logger-log.md

@@ -0,0 +1,89 @@
+---
+name: async-logger-log
+group: api
+category: async
+update-time: 20260512
+description: Enqueue a record into the async logger with an explicit level, message, optional fields, and optional target override.
+key-word:
+    - async
+    - logger
+    - log
+    - public
+---
+
+## Async-logger-log
+
+Enqueue a record into the async logger with an explicit level and message. This is the core write API behind all async level-specific convenience methods.
+
+### Interface
+
+```moonbit
+pub async fn[S] AsyncLogger::log(
+  self : AsyncLogger[S],
+  level : @bitlogger.Level,
+  message : String,
+  fields~ : Array[@bitlogger.Field] = [],
+  target? : String = "",
+) -> Unit {}
+```
+
+#### input
+
+- `self : AsyncLogger[S]` - Async logger that should receive the record.
+- `level : Level` - Severity level for the record.
+- `message : String` - Log message text.
+- `fields : Array[Field]` - Optional structured fields added to the record.
+- `target : String` - Optional per-call target override.
+
+#### output
+
+- `Unit` - No return value. The record is either skipped, enqueued, or dropped according to logger state and policy.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- The logger checks `is_enabled(level)` before building a record.
+- Context fields, patch logic, and filter logic are applied before enqueue.
+- If timestamping is enabled, `@env.now()` is captured before the record enters the queue.
+- Overflow behavior depends on the configured `AsyncOverflowPolicy`.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need A Fully Explicit Async Log Call
+
+When code should choose level, fields, and target per event:
+```moonbit
+await logger.log(
+  @bitlogger.Level::Info,
+  "worker started",
+  fields=[@bitlogger.field("job", "sync")],
+  target="service.worker",
+)
+```
+
+In this example, all per-record inputs are supplied explicitly.
+
+#### When Build Higher-level Async Logging Helpers
+
+When application code wants a custom wrapper around the base API:
+```moonbit
+await logger.log(@bitlogger.Level::Warn, "slow request")
+```
+
+In this example, `log(...)` acts as the common primitive under custom wrappers or convenience methods.
+
+### Error Case
+
+e.g.:
+- If the level is below the current minimum threshold, the record is skipped before queue insertion.
+
+- If the logger is closed or overflow policy rejects the record, enqueue may not proceed as a normal accepted write.
+
+### Notes
+
+1. Use this API when the call site needs full control instead of a fixed severity helper.
+
+2. Prefer `info()`, `warn()`, and the other shortcuts when only the level differs.