chore(internals): drop no-std supp in internals

[ZocoLini]

Summary by CodeRabbit

• Refactor
  • Simplified feature configuration across crates by removing conditional feature gates for standard library and allocation support.
  • Hex display methods (to_lower_hex_string, to_upper_hex_string, to_hex_string, append_hex_to_string) are now always available instead of being conditionally compiled.

[coderabbitai]

📝 Walkthrough

Walkthrough

The PR removes no_std support and simplifies feature flags across the internals crate and its dependents. Feature-gated std and alloc are eliminated from internals/Cargo.toml, feature references are removed from dash and hashes Cargo.toml files, and conditional compilation gates are removed from internals source code to make alloc/std functionality unconditional.

Changes

Cohort / File(s)	Summary
Cargo Feature Configuration dash/Cargo.toml, hashes/Cargo.toml, internals/Cargo.toml	Removed internals/std and internals/alloc feature dependencies; eliminated std and alloc feature definitions from internals/Cargo.toml, converting from feature-gated to always-enabled setup.
Conditional Compilation Removal internals/src/hex/display.rs, internals/src/lib.rs	Removed \#\[cfg(feature = "alloc")\] gates from DisplayHex methods and tests; removed no_std attribute and internal prelude module; simplified type paths from alloc::vec::Vec<u8> to Vec<u8>; flattened test module structure.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Poem

🐰 We've tidied up the feature gates,
No more no_std allocates!
The internals now stand clear,
With std support sincere,
Simpler code, as futures awaits! ✨

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: removing no_std support from the internals crate, which is the primary objective across all modified files.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

• 📝 Generate docstrings (stacked PR)
• 📝 Generate docstrings (commit on current branch)

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch chore/drop-nostd-internals

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@internals/src/hex/display.rs`:
- Around line 272-324: Add a unit test that exercises the newly added impl
DisplayHex for &Vec<u8> directly (current tests only call the &[u8] path via
check_encoding), e.g., add a test function (similar to existing tests like
single/two) that constructs a Vec<u8> and calls check_encoding on a reference to
it so the &Vec<u8> impl is used; reference the check_encoding helper and the
DisplayHex impl for &Vec<u8> when locating where to add the test in this file.

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: b1841341-591e-49c0-b65d-57d7bc2ef026

📥 Commits

Reviewing files that changed from the base of the PR and between 9959201 and 4410fb6.

📒 Files selected for processing (5)

• dash/Cargo.toml
• hashes/Cargo.toml
• internals/Cargo.toml
• internals/src/hex/display.rs
• internals/src/lib.rs

💤 Files with no reviewable changes (2)

• internals/Cargo.toml
• internals/src/lib.rs

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 67.14%. Comparing base (9959201) to head (4410fb6).

Additional details and impacted files

@@              Coverage Diff              @@
##           v0.42-dev     #519      +/-   ##
=============================================
+ Coverage      66.82%   67.14%   +0.32%     
=============================================
  Files            313      313              
  Lines          64756    64757       +1     
=============================================
+ Hits           43272    43484     +212     
+ Misses         21484    21273     -211     

Flag	Coverage Δ		*Carryforward flag
core	74.93% <100.00%> (ø)
dash-network	74.89% <ø> (-0.04%)	⬇️	Carriedforward from 9959201
dash-network-ffi	34.74% <ø> (ø)		Carriedforward from 9959201
dash-spv	68.28% <ø> (ø)		Carriedforward from 9959201
dash-spv-ffi	34.74% <ø> (ø)		Carriedforward from 9959201
dashcore	74.89% <ø> (-0.04%)	⬇️	Carriedforward from 9959201
dashcore-private	74.89% <ø> (-0.04%)	⬇️	Carriedforward from 9959201
dashcore-rpc	19.92% <ø> (ø)		Carriedforward from 9959201
dashcore-rpc-json	19.92% <ø> (ø)		Carriedforward from 9959201
dashcore_hashes	74.89% <ø> (-0.04%)	⬇️	Carriedforward from 9959201
ffi	40.32% <ø> (+5.07%)	⬆️
key-wallet	65.69% <ø> (ø)		Carriedforward from 9959201
key-wallet-ffi	34.74% <ø> (ø)		Carriedforward from 9959201
key-wallet-manager	65.69% <ø> (ø)		Carriedforward from 9959201
rpc	19.92% <ø> (ø)
spv	81.12% <ø> (-0.03%)	⬇️
wallet	65.69% <ø> (ø)

*This pull request uses carry forward flags. Click here to find out more.

Files with missing lines	Coverage Δ
internals/src/hex/display.rs	87.50% <100.00%> (+0.10%)	⬆️

... and 14 files with indirect coverage changes

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