Show toolchain paths in rustup show -v output

[CLoaKY233]

This PR implements the feature requested in issue #3408 by adding path information for each installed toolchain when using the -v verbose flag with rustup show.

Changes

1. Modified the show function in src/cli/rustup_mode.rs to display the path for each installed toolchain in verbose mode
2. Now all toolchains show their paths in the detailed output, not just the active toolchain

Before

installed toolchains
--------------------
stable-x86_64-pc-windows-msvc (active, default)
  rustc 1.85.1 (4eb161250 2025-03-15)

1.81-x86_64-pc-windows-msvc
  rustc 1.81.0 (eeb90cda1 2024-09-04)

After

installed toolchains
--------------------
stable-x86_64-pc-windows-msvc (active, default)
  rustc 1.85.1 (4eb161250 2025-03-15)
  path: C:\Users\laysh\.rustup\toolchains\stable-x86_64-pc-windows-msvc

1.81-x86_64-pc-windows-msvc
  rustc 1.81.0 (eeb90cda1 2024-09-04)
  path: C:\Users\laysh\.rustup\toolchains\1.81-x86_64-pc-windows-msvc

Fixes #3408

[rami3l]

Thanks a lot for the contribution!

Before merging this PR, could you please squash these changes into one commit? Many thanks in advance 🙏

[CLoaKY233]

@rami3l changes made, and commits squashed, any changes you suggest?

[djc]

Makes sense to me, thanks!

[rami3l]

@CLoaKY233 Thanks for your contribution, and LGTM!