feat(cheats)!: remove readFork cheatcodes

[0xrusowsky]

This PR is a follow-up of the ongoing effort to improve multichain scripting workflows:

refs:

• Native Multichain Scripting Workflow #11078
• feat(cheats): setup config env vars #11236
• feat(cheats): support arrays + rename read + resolve env vars #11302
• feat(config): support numeric keys in [fork.<chain>] section #11340

Motivation

Currently, storing deployment addresses and params in a easy to reuse and automate manner is cumbersome and requires dealing with ffi and json/toml cheatcodes (having to manipulate entire files)

This PR build on the previously introduces readFork cheatcodes to help ease the deployment process even further.

Solution

This PR introduces writeFork cheatcodes that enable tests and scripts to persist deployment
addresses and configuration data to a dedicated TOML file, separate from foundry.toml. This provides a safe, controlled way to maintain deployment state across test runs without risking corruption of the main configuration file.

New Cheatcodes:

Check Operations:

• checkForkVar(string key): check if a key exists for the active fork
• checkForkChainVar(uint256 chain, string key): check if a key exists for a specific chain

Write Operation:

only possible when scripting, update memory and disk, return (bool success, bool overwritte)

• writeForkVar(string key, <type> value): write to active fork configuration
• writeForkChainVar(uint256 chain, string key, <type> value): write to specific chain configuration

Dedicated config file:

• fork configurations are now stored in a separate TOML file (i.e. deployments.toml) specified via [forks].path in foundry.toml
• this file cannot be foundry.toml nor the inheritance file informed in extends
• similar to ffi, users decide whether to give write access to foundry (defaults to read-only)

  # foundry.toml
  [forks]
  path = "deployments.toml"  # Path to dedicated fork config file
  access = "read-write"      # Optional tonable write access (defaults to "read")

  # deployments.toml
  [mainnet]
  rpc_endpoint = "..."

  [mainnet.vars]
  weth = "0x..."
  deployed_contract = "0x..."