refactor: Move mock files to test folder

[zguesmi]

This PR cleans the makefile and removes the current implementation of upgrade scripts because scripts are intended to be used on live networks and for production, it does not make sens to use mock files in them.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (main@03ba891). Learn more about missing BASE report.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #73   +/-   ##
=======================================
  Coverage        ?   83.78%           
=======================================
  Files           ?        4           
  Lines           ?      111           
  Branches        ?        7           
=======================================
  Hits            ?       93           
  Misses          ?       17           
  Partials        ?        1           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[Le-Caignec]

`vm.getCode` only looks for code in the src folder. This breaks all our upgrade scripts that rely on mock files for upgrades.

run : make upgrade-on-anvil

[zguesmi]

vm.getCode only looks for code in the src folder. This breaks all our upgrade scripts that rely on mock files for upgrades.
run : make upgrade-on-anvil

@Le-Caignec see the PR description.

[Copilot]

Pull Request Overview

Refactors project structure to move mock contracts under test directories and disables mock-based upgrade scripts to avoid accidental use in production workflows. Also renames several Makefile targets and aligns documentation references accordingly.

• Relocated mock imports to point to src instead of previous relative mock paths
• Disabled Upgrade scripts by replacing logic with a reverting stub
• Renamed Makefile targets (e.g., upgrade-* and send-tokens-*) and updated README/docs accordingly

Reviewed Changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
test/units/mocks/RLCLiquidityUnifierV2Mock.sol	Updated import path to source contract
test/units/mocks/IexecLayerZeroBridgeV2Mock.sol	Updated import path to source contract
test/units/bridges/layerZero/IexecLayerZeroBridgeUpgradeScript.t.sol	Adjusted mock import path for test usage
test/units/RLCLiquidityUnifierUpgrade.t.sol	Reordered/updated import to relocated mock
script/bridges/layerZero/IexecLayerZeroBridge.s.sol	Removed live upgrade logic; now reverts
script/SendFromEthereumToArbitrum.s.sol	Clarified network scope in comment
script/SendFromArbitrumToEthereum.s.sol	Clarified network scope in comment
script/RLCLiquidityUnifier.s.sol	Removed live upgrade logic; now reverts
script/RLCCrosschainToken.s.sol	Added placeholder Upgrade contract that reverts
docs/soldoc/src/README.md	Updated Make targets references
README.md	Updated Make targets references
Makefile	Reorganized deployment/upgrade/config targets; renamed and added targets

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}