Make Builtins.unsafeUncons use builtin list casing

[sohang3112]

avoid seperate head, tail calls in Builtins.unsafeUncons. No Changelog Required. Fixes #7459

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[sohang3112]

@ana-pantilie Can you review this PR please? Or if someone else would be correct reviewer, let me know - not sure who to tag here.

[sohang3112]

Also I'm not sure why ci/eval action is failing with timeout, seems to be some issue with Github CI itself maybe:

'nix flake metadata' returned signal -1:
unpacking 'github:IntersectMBO/plutus/8c12795478d0bf9842a74fabab96c1704a14633e' into the Git cache...
timeout

[ana-pantilie]

@sohang3112 I've tagged @SeungheonOh as the reviewer and I've approved the GitHub Workflows to run.

[sohang3112]

@SeungheonOh Please review this PR. Also re the failing CI checks:

• Changelog action failed, it says to apply label "No Changelog Required" but I don't seem to have permission to apply label to issue as I am external contributor to this repo. Please apply label "No Changelog Required" to this issue on your end.
• ci/eval is failing with timeout. It's totally unrelated to code and may be some bug in Github Action itself, please check:

'nix flake metadata' returned signal -1:
unpacking 'github:IntersectMBO/plutus/8c12795478d0bf9842a74fabab96c1704a14633e' into the Git cache...
timeout

[sohang3112]

@ana-pantilie ci/eval action got stuck initially at "Awaiting approval from a maintainer" and then timed out after a few minutes. Do you know what is the fix for this - can you provide whatever approvals are necessary here?

[SeungheonOh]

Hi, my apologies for delay.

This PR doesn't do what I described in the issue. This reuses PlutusTx.Builtins.Internal.caseList' which will generate

--pseudo plc
case <list>
  <cons branch : x -> list x -> r>
  <nil branch : r>

For this, since we are casing the cons case only, instead of generating case with both cons branch and nil branch, it can omit nil branch and do something like

case <list>
  <cons branch : x -> list x -> r>

which will fail if empty list is given.

To accomplish this, one need to add new builtin to PlutusTx.Builtins.Internal and add support to the added builtin in PlutusTx.Plugin.Builtins. Check how it's done for caseList'.

[sohang3112]

@SeungheonOh As per your feedback, I have created a new builtin unsafeCaseList' in PlutusTX.Builtins.Internal and used it to define Builtins.unsafeCons. Please review whether it is correct now.

[ana-pantilie]

Hi @sohang3112, thanks for your contribution but please be patient, Seungheon is on PTO so he'll answer when he gets back.

[SeungheonOh]

Hi, thanks for the change. This is a correct direction; however this won't actually compile because it doesn't provide accompanying definition in PlutusTx.Plugin.Builtins.

Also please add a test case.