In this commit, we strip all of the local `replace ... => ../...`
directives that were introduced as part of #1825 (the v2 module
restructuring), now that proper tags exist for every freshly carved-out
submodule. Every in-tree go.mod is pinned to the newly published tags:
chainhash/v2.0.0, wire/v2.0.0, chaincfg/v2.0.0, address/v2.0.0,
txscript/v2.0.0, btcutil/v2.0.0, psbt/v2.0.0, and btcec is bumped to
v2.5.0 since it now depends on chainhash/v2 (previously
chaincfg/chainhash).
While here, we also unify the Go toolchain to 1.25 across every
submodule so the workspace resolves a consistent set of language
features.
Finally, we bump the main btcd version to v0.26.0-beta.rc1 in
preparation for the upcoming release candidate.
