feat(config): add remappings_scope option for global remappings

[Ubuntu-Buddha]

Summary

Adds a remappings_scope config option that controls whether dependency remappings are included when loading config. When set to global, only project-level remappings are used and remappings from nested foundry.toml files in dependencies are ignored.

This addresses the issue where Soldeer and similar package managers have dependencies that ship their own remappings.txt files pointing to node_modules/ paths which don't exist in the project.

Changes

• Add RemappingsScope enum (Default | Global) in crates/config/src/lib.rs
• Add remappings_scope field to Config struct (default: Default)
• Update RemappingsProvider to skip find_nested_foundry_remappings() when scope is Global
• Add test test_remappings_scope_global_ignores_dependency_remappings

Usage

[profile.default]
remappings_scope = "global"
remappings = ["@dep/=lib/dep/"]

With this config, remappings defined in lib/dep/foundry.toml are ignored, and only the project's remappings are used.

Test Plan

• Added unit test verifying dependency remappings are excluded when remappings_scope = "global"
• All existing config tests pass (141 unit tests + 19 doctests)

Closes #12420