feat: itests: add itests ensemble mocknet getter

[elijaharita]

Related Issues

We want FilClient to use itests ensemble for tests. It requires access to the mocknet object inside of ensemble, so that it can hook into the offline network, which is currently private.

Proposed Changes

Add a public getter for itests ensemble mocknet.

Additional Info

Checklist

Before you mark the PR ready for review, please make sure that:

• All commits have a clear commit message.
• The PR title is in the form of of <PR type>: <area>: <change being made>
  • example: fix: mempool: Introduce a cache for valid signatures
  • PR type: fix, feat, INTERFACE BREAKING CHANGE, CONSENSUS BREAKING, build, chore, ci, docs,perf, refactor, revert, style, test
  • area: api, chain, state, vm, data transfer, market, mempool, message, block production, multisig, networking, paychan, proving, sealing, wallet, deps
• This PR has tests for new functionality or change in behaviour
• If new user-facing features are introduced, clear usage guidelines and / or documentation updates should be included in https://lotus.filecoin.io or Discussion Tutorials.
• CI is green

[codecov]

Codecov Report

Merging #8157 (e2a93a3) into master (9429229) will decrease coverage by 0.01%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #8157      +/-   ##
==========================================
- Coverage   39.48%   39.46%   -0.02%     
==========================================
  Files         666      666              
  Lines       72498    72500       +2     
==========================================
- Hits        28627    28615      -12     
- Misses      38915    38928      +13     
- Partials     4956     4957       +1     

Impacted Files	Coverage Δ
itests/kit/ensemble.go	90.76% <0.00%> (-0.49%)	⬇️
cli/util.go	41.66% <0.00%> (-8.34%)	⬇️
markets/retrievaladapter/client_blockstore.go	62.50% <0.00%> (-6.25%)	⬇️
chain/actors/builtin/miner/diff.go	52.94% <0.00%> (-5.89%)	⬇️
chain/types/tipset_key.go	85.96% <0.00%> (-3.51%)	⬇️
node/hello/hello.go	63.63% <0.00%> (-3.41%)	⬇️
chain/exchange/client.go	52.96% <0.00%> (-1.70%)	⬇️
blockstore/autobatch.go	56.30% <0.00%> (-1.69%)	⬇️
miner/miner.go	56.72% <0.00%> (-1.32%)	⬇️
chain/stmgr/searchwait.go	68.58% <0.00%> (-1.29%)	⬇️
... and 13 more

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