Tune TokenPool contracts to make it compatible with gho-core

[miguelmtzinf]

Modifications:

• Soften Solidity compiler version of TokenPool contracts to ^0.8.0 so they are compatible with gho-core.
• Remove named parameters in mapping types (as it was introduced in v0.8.18).
• Makes _transferOwnership internal instead of private so it's possible to initialize the owner outside the constructor.

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[github-actions]

LCOV of commit 861a21b during Solidity Foundry #1

Summary coverage rate:
  lines......: 98.7% (936 of 948 lines)
  functions..: 95.6% (196 of 205 functions)
  branches...: 91.9% (364 of 396 branches)

Files changed coverage rate: n/a