What?

This change adds first-class support for list-based syntax in DAG-Factory YAML:

1. Tasks as a list
2. Task Groups as a list

Until now, both sections had to be dictionaries keyed by task_id / group_id. Authors can now opt for a cleaner, order-preserving list format while everything still works in dictionary form.

Why?

The list style is more natural, readable, and aligns with common YAML patterns.

Example before ⬇️

tasks:
  task_1:
    operator: airflow.operators.bash.BashOperator
    bash_command: "echo 1"

Example after ⬇️

tasks:
  - task_id: task_1
    operator: airflow.operators.bash.BashOperator
    bash_command: "echo 1"

Same goes for task_groups:

task_groups:
  - group_name: extract
    tooltip: "extraction steps"

Implementation details

DagBuilder.build() now:
Detects if tasks or task_groups is a list.
Converts each list to the existing dict structure (task_id / group_name key becomes dict key).
Performs validation:

1. Each entry must be a mapping with the required identifier field.
2. Duplicate identifiers raise DagFactoryConfigException.
   No downstream code had to change – all later logic still sees a dictionary.

Backwards compatibility

Existing dictionary syntax continues to work unchanged.
Tests covering legacy pattern remain green.

closes: #468