…nts (#18384)

## What does this PR do?

Extracts all `"aws.durable.*"` span name string literals from `patch.py` into named constants in `ddtrace/ext/aws_durable.py`, then replaces every bare literal with the corresponding constant.

**New constants added to `ddtrace/ext/aws_durable.py`:**
- `SPAN_STEP`
- `SPAN_WAIT`
- `SPAN_WAIT_FOR_CONDITION`
- `SPAN_WAIT_FOR_CALLBACK`
- `SPAN_CREATE_CALLBACK`
- `SPAN_MAP`
- `SPAN_PARALLEL`
- `SPAN_CHILD_CONTEXT`

## Motivation

Addresses [reviewer feedback](#18191 (comment)) on #18191: span name strings should be constants rather than bare literals so they are defined in one place and typos are caught at import time.

## Testing

No behavior change — span names are identical. Existing integration tests cover the affected code paths.

Co-authored-by: yiming.luo <[email protected]>

…erations span (#18191)

## Description

Add `aws.durable.operation_attempt` to `aws.durable.step` and `aws.durable.wait_for_condition` spans. The value is 0-indexed: 0 = original attempt, 1 = first retry, 2 = second retry, etc.

Sourced from the Durable Execution SDK's `StepDetails.attempt` field in the operation checkpoint, passed through directly. When no checkpoint exists yet (first execution, no prior failures), the tag defaults to `0`.

This tag will be used by UI to display attempt count and group attempts for the same operation.

## Testing
Installed the tracer on a durable function and invoked it.

The `aws.durable.step` span for `order_verify_inventory` operation failed twice the succeeded.

For the original attempt, the tag has a value of 0.
<img width="653" height="209" alt="image" src="https://github.com/user-attachments/assets/e58c4904-1d9c-4665-9ef5-0e4a56712144" />

1st retry (2nd attempt): `aws.durable.operation_attempt` is 1.
<img width="639" height="207" alt="image" src="https://github.com/user-attachments/assets/9bdf61f0-d842-4370-ab4b-4fe0238fc34e" />

2nd retry (3rd attempt): `aws.durable.operation_attempt` is 2.
<img width="649" height="194" alt="image" src="https://github.com/user-attachments/assets/c6e8f398-8a82-4513-a3e5-016379017888" />

[Link for you to check them yourself](https://dd.datad0g.com/apm/traces?query=service%3Ayiming-durable-py-custom-tracer&agg_m=count&agg_m_source=base&agg_t=count&cols=service%2Cresource_name%2C%40duration%2C%40http.method%2C%40http.status_code%2C%40_span.count%2C%40_duration.by_service&fromUser=false&graphType=flamegraph&historicalData=true&messageDisplay=inline&query_translation_version=v0&refresh_mode=paused&shouldShowLegend=true&sort=desc&spanType=all&storage=hot&traceQuery=&view=spans&start=1779812280000&end=1779812340000&paused=true)

### Why only `step` and `wait_for_condition` spans?

The SDK has six `OperationExecutor` subclasses; only two use the `StepDetails.attempt` retry mechanism:

| Executor | Detail field on checkpoint | Has retry? |
|---|---|---|
| `StepOperationExecutor` | `step_details` | yes |
| `WaitForConditionOperationExecutor` | `step_details` (polling iterations) | yes |
| `CallbackOperationExecutor` | `callback_details` | no |
| `InvokeOperationExecutor` | `chained_invoke_details` | no |
| `ChildOperationExecutor` | — | no |
| `WaitOperationExecutor` | `wait_details` | no |

`wait_for_callback` isn't its own executor — it's a helper that internally calls `create_callback` + `step`, so any retries appear on the inner `aws.durable.step` child span (already covered). `map` and `parallel` also have no executor; their work is decomposed into MAP_ITERATION / PARALLEL_BRANCH child operations, which `_is_top_level_for_span` filters out anyway.

Co-authored-by: yiming.luo <[email protected]>