feat: nv28 skeleton

[rjan90]

closes: #2219

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.58%. Comparing base (c414105) to head (a79aceb).
⚠️ Report is 20 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2220   +/-   ##
=======================================
  Coverage   77.58%   77.58%           
=======================================
  Files         147      147           
  Lines       15789    15789           
=======================================
  Hits        12250    12250           
  Misses       3539     3539           

Files with missing lines	Coverage Δ
fvm/src/gas/price_list.rs	85.59% <ø> (ø)
fvm/src/machine/default.rs	69.47% <ø> (ø)
shared/src/version/mod.rs	0.00% <ø> (ø)

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[rjan90]

For unblocking this PR/get past the #2221 failure in cargo-deny, I suggest to either:

• Address it separately (i.e merge even with the failure) or update the deny.toml config to allow this temporarily.
• Update wasmtime to a newer version (update wasmtime to at least 33.0.2 #2186) that doesn't use fxhash.
  • This might require significant changes.

[BigLep]

Do you have a recommendation @rvagg ?

[rvagg]

I'm fine with merging this as is, but also you could just update deny.toml in here since you've opened an issue for the problem already.

[Copilot]

Pull Request Overview

This PR introduces a skeleton for network version 28 (nv28) by adding the necessary version constant and conditional compilation support. The changes prepare the codebase for future nv28 development while keeping it behind a feature flag.

• Adds V28 network version constant alongside updating the comment for V27
• Implements conditional compilation to support nv28 when the nv28-dev feature is enabled
• Configures gas pricing for nv28 to use the existing TEEP_PRICES structure

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
shared/src/version/mod.rs	Adds V28 constant and updates V27 comment from TBD to GoldenWeek
fvm/src/machine/default.rs	Conditionally extends supported version range to include V28
fvm/src/gas/price_list.rs	Adds V28 gas pricing support using existing TEEP_PRICES
fvm/Cargo.toml	Introduces nv28-dev feature flag

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