refactor: migrate package management from poetry to pep 621 standard

Migrate package metadata and dependency configuration from Poetry to
PEP 621 standard using flit_core backend. Update documentation with
production and development setup instructions using venv, pip, or uv.

- update pyproject.toml to PEP 621 format with flit_core build-system
- bump minimum dependency versions to latest PyPI releases
- revise README.md with production and development setup guides

README.md

@@ -2,10 +2,42 @@
 
 The mdrs-client-python is python library and a command-line client for up- and downloading files to and from MDRS based repository.
 
-## Installing
+## Installation (Production)
+
+It is recommended to use a virtual environment (`venv`) to keep your Python environment isolated.
+
+### Option 1: Using standard `venv` + `pip`
 
 ```shell
-poetry install
+python3 -m venv .venv
+source .venv/bin/activate  # On Windows: .venv\Scripts\activate
+pip install .
+```
+
+### Option 2: Using `uv`
+
+```shell
+uv venv
+source .venv/bin/activate  # On Windows: .venv\Scripts\activate
+uv pip install .
+```
+
+## Development Setup
+
+To set up a local development environment with development tools (testing, formatting, linting):
+
+### Option 1: Using standard `venv` + `pip`
+
+```shell
+python3 -m venv .venv
+source .venv/bin/activate  # On Windows: .venv\Scripts\activate
+pip install -e ".[dev]"
+```
+
+### Option 2: Using `uv` (Recommended for developers)
+
+```shell
+uv sync
 ```
 
 ## CLI Usage