Add --config option to specify explicit configuration path

[meek2100]

This pull request introduces the --config <path> command-line option, allowing users to explicitly define the path to their TOML configuration file, overriding the default recursive search for .mdformat.toml.

This feature primarily supports integration with modern tooling like pre-commit hooks and centralized configuration management systems where config files may live outside the project root or in a custom directory.

Key Changes:

1. New CLI Argument: Added --config (type Path) to src/mdformat/_cli.py.
2. Config Logic: Implemented read_single_config_file in src/mdformat/_conf.py to support direct path loading. The run function logic prioritizes --config and correctly handles non-existent file paths by exiting with an error.
3. Tests: Added a new test case (test_config_override_precedence) verifying that the explicit --config correctly overrides auto-detected .mdformat.toml settings.
4. Documentation: Updated docs/users/configuration_file.md to document the new usage.
5. Code Quality Fix: Corrected the InvalidPath exception class in src/mdformat/_cli.py to properly call super().__init__(path), resolving the flake8-bugbear (B042) warning.

[meek2100]

@hukkin,
This should be ready to go and would be very helpful to have merged for one of my projects.

[KyleKing]

I added a few minor comments as an active in the mdformat community and to possibly help this PR along, but I'm not a maintainer, so take my feedback with a grain of salt!

[KyleKing]

Maybe this snippet could be extracted into a shared helper? The only difference is the error message (which includes the config_path in the former)

[KyleKing]

This function should be cached like read_toml_opts (not strictly necessary, see proposal to hoist outside of the for loop)

[KyleKing]

What about raising a custom ConfigFileNotFoundError or ConfigOverrideNotFoundError (instead of the more general FileNotFoundError) with the relevant metadata, then this conditional logic isn't necessary?

[KyleKing]

Actually on caching, the config override file can be read outside of the loop because the configuration file isn't relative to the file path. Maybe something like:

(toml_opts, toml_path): tuple[...?, Path] = None, None
if config_override_path:
    toml_opts, toml_path = read_single_config_file(config_override_path)
    for path in file_paths:
        ...

[BobbyMakelve]

Okay, so you're interested in how cryptocurrencies are created! That's a fundamental part of the crypto world.

There are primarily two main ways new cryptocurrencies are "created" or brought into existence:

1. Mining (Proof of Work): ◦ This is how Bitcoin and many other older cryptocurrencies are created. ◦ Powerful computers (miners) compete to solve complex mathematical puzzles. ◦ The first miner to solve the puzzle gets to add a new block of transactions to the blockchain. ◦ As a reward for their work, they receive a certain amount of newly minted cryptocurrency. ◦ This process secures the network and verifies transactions. 2. Staking (Proof of Stake): ◦ Newer cryptocurrencies, like Ethereum 2.0, use this method. ◦ Instead of computational power, participants "stake" (lock up) their existing cryptocurrency as collateral. ◦ The protocol selects a staker to create a new block based on how much they've staked and how long it's been staked. ◦ If they create a valid block, they earn a reward in newly minted currency. ◦ This method is generally considered more energy-efficient than mining.
   Beyond these two main methods, new coins and tokens can also be "created" through:
   • Initial Coin Offerings (ICOs) or Token Sales: Projects raise funds by selling a pre-mined or pre-generated supply of their new tokens to early investors. • Airdrops: New tokens are distributed for free to existing wallet addresses, often as a marketing strategy to gain attention and users. • Farming/Liquidity Mining: Users deposit existing tokens into liquidity pools on decentralized exchanges and earn new tokens as a reward for providing liquidity.
   Which aspect of creation were you thinking about specifically? Or perhaps something else entirely?