test: make runtime compatibility fixtures resilient to protocol bumps (#2908)

## Summary
- Fix the stale compatibility fixtures causing the TypeScript, Python,
and Go failures on release PR #2798.
- Derive incompatible runtime versions from the current protocol major
instead of hardcoding `2.0.0`.
- Use the current protocol version for Go compatible/wrong-runtime
fixtures; keep explicit-version protocol comparison tests unchanged.
- Test-only changes. No runtime behavior or release version changes.

## Why
The release bumps the protocol from `1.0.0` to `2.0.0`. Tests that
previously treated `2.0.0` as incompatible start accepting it, while the
Go fixture treating `1.0.9` as compatible starts rejecting it. Deriving
the fixtures from the current protocol avoids repeating this failure on
future major releases.

## Validation
Passed with both the main protocol version (`1.0.0`) and a temporary
release-equivalent bump (`2.0.0`) applied to the protocol package and
generated Go/Python constants:
- TypeScript: `pnpm exec vitest run
packages/sdk-ts/tests/cdpClientLifecycle.test.ts` — 19 passed.
- Python: `uv run --locked pytest tests/test_cdp_client.py -q` — 28
passed.
- Go: `go test . -run
'Test(NegotiateRuntimeCompatibility|ProtocolCompatibility)$' -count=1` —
passed.

Also passed TypeScript oxfmt/oxlint, Python Ruff lint/format, Go gofmt,
and `git diff --check`.

Temporary version bumps were reverted before committing. Full CI remains
to run on this PR.

Merge this into main so the release PR can incorporate the corrected
fixtures.

<!-- This is an auto-generated description by cubic. -->
---
## Summary by cubic
Fixes the stale runtime compatibility fixtures in the TypeScript,
Python, and Go SDK tests that break when the protocol version bumps.
Fixtures now derive incompatible versions from the current protocol
major instead of hardcoding `2.0.0`.

- Go fixtures use the current `stagehandProtocolVersion` for compatible
and wrong-runtime cases and compute the next major for the mismatch
case.
- Python and TypeScript tests derive the incompatible version as the
current protocol major plus one.
- Test-only change; no runtime behavior or release version changes.

<sup>Written for commit 46e7d4ab25f160e0a86487d456bff934aba684bb.
Summary will update on new commits.</sup>

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