remove datetime and only use pandas Timestamp class

[adrianhasse]

• adjust variable names from datetime / date to timestamp
• use pandas.Timestamp not datetime.datetime
• introduce devcontainer

[Copilot]

Pull Request Overview

This PR standardizes all date/time handling by removing datetime in favor of pd.Timestamp and introducing a development container setup.

• Renamed parameters, variables, and attributes from date/datetime to timestamp and unified on pd.Timestamp.
• Removed all datetime.datetime imports and updated docstrings to reflect the new naming.
• Added a .devcontainer configuration for a consistent development environment.

Reviewed Changes

Copilot reviewed 11 out of 12 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tests/test_strategy.py	Updated generate_orders signature to accept current_timestamp.
tests/test_integration.py	Renamed current_date parameter to current_timestamp.
tests/test_entities.py	Removed datetime import and switched to timestamp fields.
tests/test_broker.py	Changed all datetime usages to timestamp and updated tests.
tests/conftest.py	Renamed fixture index from date to timestamp.
kissbt/strategy.py	Adjusted method signature and docs to use current_timestamp.
kissbt/entities.py	Renamed datetime fields in OpenPosition/ClosedPosition.
kissbt/engine.py	Group by timestamp instead of date and call generate_orders.
kissbt/broker.py	Replaced datetime parameters with timestamp throughout.
kissbt/analyzer.py	Changed minute unit key from 'M' to 'T' and plot to timestamp.
.devcontainer/devcontainer.json	Added devcontainer setup for Python 3.13 environment.

Comments suppressed due to low confidence (2)

kissbt/broker.py:180

• In the _update_closed_positions docstring, specify the type as pd.Timestamp (e.g., timestamp (pd.Timestamp)) to maintain consistency and clarity.

            timestamp (timestamp): Timestamp of the closing/reduction

kissbt/broker.py:226

• In the _update_open_positions docstring, use the fully qualified pd.Timestamp type instead of Timestamp for clarity.

            timestamp (Timestamp): The timestamp when the position was opened or