It should be possible to update local `.tool_versions` via starkup as well

Currently, when running starkup, we only update the global (home dir) .tool_versions

https://github.com/software-mansion/starkup/blob/01a19e2f0bd0640b2a137bfe0426ce83840e9826/starkup.sh#L524-L524

However, since starkup is intended not only as one-time installer, but also an updater for all tools, it seems it would be reasonable to also allow using it ot update project's .tool_versions:

Name                  Version            Source                                    Installed
cairo-coverage        0.6.0              /Users/user/.tool-versions                true
cairo-profiler        0.16.0             /Users/user/.tool-versions                true
scarb                 nightly-2025-06-07 /Users/user/repos/starkup/.tool-versions  true
starknet-devnet       0.7.2              /Users/user/.tool-versions                true
starknet-foundry      0.59.0             /Users/user/.tool-versions                true

This can be done in various ways, for example:

1. --local flag: in this case we run asdf set without --home
2. Automatic detection of non-home .tool-versions -> if present, updates both global tools, and the tools listed in local .tool_versions (and only them) automatically

Read starkup.sh around line 524 and inspect how the global .tool_versions file is updated. Trace the existing argument parsing and update flow, then compare the proposed --local and automatic-detection behaviors. Done means the chosen behavior updates the intended local tools while preserving the existing global update behavior.