docs: version developer docs for v4.1.3 and v4.2.0-aztecnr-rc.2 (#22378)

## Summary

This PR updates the developer documentation versioning for the v4.1.3
testnet release and the v4.2.0-aztecnr-rc.2 SDK release:

- **Version bump**: Updated testnet from `v4.1.0-rc.2` to `v4.1.3`
across network config files, contract addresses, and SponsoredFPC
- **Developer docs now target v4.2.0-aztecnr-rc.2**: Both alpha and
testnet developer docs point at the new SDK version, with a combined
"Alpha / Testnet" dropdown entry
- **Operator docs**: Show combined "Alpha / Testnet (v4.1.3)" dropdown
entry
- **Version dropdown deduplication**: Fixed `docusaurus.config.js` to
handle same-version alpha/testnet gracefully (combined label, no
duplicate entries)
- **Removed old versioned docs**: Cleaned up v4.1.0-rc.2 developer +
network versioned docs and obsolete pages from v4.1.3
- **Regenerated API docs**: aztec-nr API docs, TypeScript API docs, and
CLI reference docs
- **Migration notes fixes**: Added missing `## 4.1.3` heading in
versioned docs; reordered 4.1.3 section to correct position after 4.2.0
entries in source docs
- **Contract addresses**: Updated testnet SponsoredFPC L2 address and
other v4.1.3 addresses in `networks.md`
- **Doc quality fixes**: Contract import path,
TestWallet→EmbeddedWallet, simulate() destructuring, and other review
feedback

## Test plan
- [x] `yarn build` passes with `TESTNET_TAG=4.1.3 RELEASE_TYPE=testnet`
- [x] Developer docs version dropdown shows single "Alpha / Testnet
(v4.2.0-aztecnr-rc.2)"
- [x] Operator docs version dropdown shows single "Alpha / Testnet
(v4.1.3)"
- [x] No duplicate version entries in either dropdown

Author: critesjosh

docs/developer_version_config.json

@@ -1,4 +1,4 @@
 {
   "mainnet": "v4.2.0-aztecnr-rc.2",
-  "testnet": "v4.1.0-rc.2"
+  "testnet": "v4.2.0-aztecnr-rc.2"
 }