docs: update Arc Testnet version table to v0.7.2

[sharken3948]

docs/installation.md still lists v0.6.0 as the Arc Testnet version (table and the arcup --install example). Per CHANGELOG.md, testnet node operators must use v0.7.2 since the Zero7 activation on 2026-06-18 ('Earlier versions are not supported'), and v0.7.2 is the latest published release. A new operator following the current table would install an unsupported version. Updated both references to v0.7.2.

[osr21]

Correct fix — v0.6.0 is unsupported after Zero7 and pointing new operators there would silently break their setup.

One addition worth considering: the table currently covers only node operators. Three of the v0.7.2 changes are breaking for DApp developers (not just node operators) and aren't flagged anywhere in the docs aimed at that audience:

---

1. eth_estimateGas / eth_call gas cap lowered from 50M → 30M

Any call or simulation that previously relied on the higher cap will now fail with execution reverted once the node returns an error at 30M. This is directly connected to the eth_estimateGas discussion in #198: a correct ABI is necessary but not sufficient — the estimated gas must also fit within the 30M cap. Hardcoded gas limits or cached estimates obtained from a pre-v0.7.2 node (cap = 50M) that landed between 30M and 50M will silently start failing.

2. Precompile gas cost change: "Charge gas before performing storage I/O in precompile helpers"

The CallFrom precompile (used by Memo) and any other precompile that touches storage now charges gas at a different point in execution. Gas estimates obtained against a v0.6.x node for precompile-heavy transactions (Memo subcalls, CCTP TokenMessengerV2 calls) may be too low when submitted to a v0.7.2 node. DApps that cached or hardcoded gas limits for these paths should re-estimate against the updated node.

3. JSON-RPC batch cap: 100 entries

viem's default transport sends batched JSON-RPC calls. A page load that fires many simultaneous eth_call queries (e.g. reading multiple contract slots at once — common in dashboard views) can silently tip over 100 entries and get back a -32600 error for the entire batch, with no per-request error. DApps using createPublicClient with the default batch transport should either set batch: { batchSize: 100 } explicitly or switch to a non-batching transport if their query fan-out exceeds the cap:

import { createPublicClient, http } from 'viem'

const client = createPublicClient({
  transport: http(ARC_RPC_URL, {
    batch: { batchSize: 99 },   // stay under the 100-entry cap
  }),
})

---

All three are observable by DApp teams upgrading their target testnet node version — none are in the current installation or developer docs. Might be worth a short "Breaking changes for DApp developers" callout in docs/installation.md alongside the version table, or a link to BREAKING_CHANGES.md#v072 from the developer-facing docs.