docs: update Arc Testnet version to v0.7.3

[fidantr16]

Summary

• Update the Arc Testnet version from v0.6.0 to v0.7.3.
• Update the arcup --install command to use v0.7.3.

This keeps the installation documentation aligned with the current Arc Testnet version.

[osr21]

The version bump itself is correct, but this change is already fully covered by two older open PRs, so it's likely to close as a duplicate rather than merge.

The version is right

v0.7.3 is the current latest published release (checked the releases API — v0.7.3 is the newest one flagged release). Note v0.8.0 exists as a git tag but has no published release yet, so it correctly does not belong in the Versions table. CHANGELOG's top entry is also [v0.7.3]. So v0.6.0 → v0.7.3 on lines 18 and 64 is accurate.

Completeness (FYI)

Lines 18 (Versions table) and 64 (arcup --install) are the only two hardcoded v0.6.0 occurrences in docs/installation.md; every other version reference uses $ARC_VERSION / $VERSION variables. So the two-line change is complete on its own.

Overlap — this is the blocker

Two older PRs already make this exact edit:

• docs: update Arc Testnet version to v0.7.3 in installation.md #226 (docs: update Arc Testnet version to v0.7.3 in installation.md) — byte-identical diff to this one (same lines 18 + 64), opened earlier.
• docs: fix Arc Testnet version table and document v0.7.x breaking changes for DApp developers #199 (docs: fix Arc Testnet version table and document v0.7.x breaking changes...) — a superset: same table + arcup fix, plus an [!IMPORTANT] callout documenting the v0.7.x DApp-facing breaking changes (30M gas cap, 100-entry batch limit, precompile gas-accounting changes).

Since all three touch the same two lines, only one can merge; the rest will hit conflicts and close. #199 delivers the most value to readers, with #226 as the minimal equivalent of this PR. Might be worth folding effort into reviewing #199 (or #226) rather than maintaining a third identical patch. Flagging purely for coordination — the content here is correct.

[fidantr16]

Thanks for the clarification and for checking the change.

I’ll close this PR since #226 and #199 already cover the same update.

I’ll take a look at #199 and see if I can contribute there instead.