perf: optimize slice clearing operation (#78)

**Description**

This PR optimizes the initialization of slice a by replacing `a =
[]int{}` with `a = a[:0]`. This change reduces unnecessary memory
allocation and improves performance.

**Motivation**

When a is initialized with `a = []int{}`, a new, empty slice is created,
which allocates memory for the underlying array. However, if a is
already allocated with a non-zero capacity, reslicing it with `a =
a[:0]` reuses the existing underlying array, avoiding unnecessary memory
allocation.

**Benefits**

1. Reduces memory allocation and garbage collection overhead
2. Improves performance by reusing existing memory allocation
3. Simplifies code by eliminating unnecessary memory allocation

**Notes**

This optimization is safe because it is a basic and ordinary
optimization.

Signed-off-by: Young Xu <xuthus5@gmail.com>

opengemini/write.go

@@ -129,8 +129,8 @@ func (c *client) internalBatchSend(ctx context.Context, database string, resourc
 			}
 			needFlush = false
 			ticker.Reset(tickInterval)
-			points = []*Point{}
-			cbs = []WriteCallback{}
+			points = points[:0]
+			cbs = cbs[:0]
 		}
 	}
 }