Mark previewnet as transient

[janezpodhostnik]

See discussion here: https://discord.com/channels/613813861610684416/1210016175258599515/1210558298055516240

1. Previewnet is "Transient" in the sense that it gets bootstrapped by the default bootstrapping settings
2. Bootstrap with EVM by default
3. Move service account indexes by 1 because of the new EVM address that is created before them.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 56.39%. Comparing base (b9c9109) to head (05837b2).

Files	Patch %	Lines
model/flow/chain.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@                   Coverage Diff                   @@
##           feature/stable-cadence    #5448   +/-   ##
=======================================================
  Coverage                   56.39%   56.39%           
=======================================================
  Files                        1032     1032           
  Lines                      100711   100711           
=======================================================
+ Hits                        56796    56798    +2     
- Misses                      39605    39607    +2     
+ Partials                     4310     4306    -4     

Flag	Coverage Δ
unittests	56.39% <0.00%> (+<0.01%)	⬆️

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[turbolent]

CI fails for a few tests:

• TestWriteMachineAccountFiles
• TestEpochStaticTransition/TestStaticEpochTransition
• TestEpochJoinAndLeaveSN/TestEpochJoinAndLeaveSN

[jordanschalm]

Summarizing the machine account issue here:

Taking SN2 as an example, which has the following machine account file:

• Address: 0xb4bcb7e5ea8c4c64 [index 25]
• Machine account PubKey: 0x584319d80567e7b19414c1952a52b5e5a588d6170993ae84b4b655690233482c8fe9e354cf8e308b3771c04e80322b5b1dbe33fe4eeec67d8de6ea9d9dab6178

On-chain we have:

• Account 0xb4bcb7e5ea8c4c64 [index 25] has the wrong key/hashing algo
• Account 0x50db0e38fb764cbb [index 24] has pubkey 584319d80567e7b19414c1952a52b5e5a588d6170993ae84b4b655690233482c8fe9e354cf8e308b3771c04e80322b5b1dbe33fe4eeec67d8de6ea9d9dab6178, matching the machine account file

This means that the key generation is using index 25 but the machine account was actually created in index 24. Meaning that our initial index is off by +1 (5 rather than 4). So I think reverting this change will resolve the problem (it also seems to indicate the EVMStorageAccountIndex constant is wrong.

Suggested change

	addressIndex := uint64(systemcontracts.EVMStorageAccountIndex)
	addressIndex := uint64(4)

[janezpodhostnik]

it also seems to indicate the EVMStorageAccountIndex constant is wrong

That is concerning!

I will revert those changes from this PR and I will open another PR to deal with that.