Support tasks and task_groups as lists

[pankajkoti]

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

[codecov-commenter]

Codecov Report

❌ Patch coverage is 92.10526% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.70%. Comparing base (ea0ab42) to head (bdbf8df).
⚠️ Report is 127 commits behind head on main.

Files with missing lines	Patch %	Lines
dagfactory/dagbuilder.py	92.10%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #487      +/-   ##
==========================================
- Coverage   93.76%   93.70%   -0.06%     
==========================================
  Files          11       11              
  Lines        1042     1080      +38     
==========================================
+ Hits          977     1012      +35     
- Misses         65       68       +3     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[pankajkoti]

I have logged a follow-up ticket: #491 to update example DAGs and docs to reflect authoring tasks as list. Will work on a quick follow-up PR to do that once this change is avaialble and merged. Keeping the scope of this PR limited to ease reviews.

[tatiana]

This is a very exciting feature, and it's great it is backwards compatible.
I left an implementation feedback inline, but happy with the feature!