Add iter(), iter_mut(), drain(), and clear()

[nixonyh]

• Add iter() & iter_mut() to iterate through the entire map (unordered)
• Add drain() to drain the entire map while iterating through the values.
• Add clear() to clear all values and invalidate existing keys (via generation incrementation).
• Bumped version to 0.3.0

[coderabbitai]

📝 Walkthrough

Walkthrough

This PR extends SparseMap with live-value iteration and bulk removal APIs. New public methods iter(), iter_mut(), drain(), and clear() are added alongside a Drain<'a, T> iterator type. The draining iterator removes and invalidates entries as it traverses, with generation-aware slot recycling. Tests verify iteration, generation-based key invalidation, slot reuse, and early-drop behavior. Version bumped to 0.3.0.

Changes

SparseMap iteration and bulk removal APIs

Layer / File(s)	Summary
API contract and version update Cargo.toml, src/lib.rs (231–277)	New public methods iter(), iter_mut(), drain(), and clear() declared on SparseMap<T>. Version incremented from 0.2.0 to 0.3.0.
Drain iterator implementation src/lib.rs (279–312)	Drain<'a, T> struct and Iterator impl remove occupied slots on each next(), bumping generations and updating the free-slot list. Drop impl ensures cleanup if iteration exits early.
Tests for iteration and bulk removal src/lib.rs (591–678)	Tests verify iter()/iter_mut() behavior, drain() yields all entries and enables slot reuse while preventing stale-key reuse via generation bumping, clear() empties and invalidates keys, and early-drop of the draining iterator completes cleanup.

🎯 3 (Moderate) | ⏱️ ~25 minutes

🐰 With iter() and drain() now flowing,
And clear() slots brightly glowing,
No values lost to generation's test,
The SparseMap now performs its best! 🗺️✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately and clearly summarizes the main changes, listing the four new methods being added to the API.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description check	✅ Passed	The pull request description clearly describes the changeset, listing the four main additions: iter(), iter_mut(), drain(), and clear() methods, plus version bump.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

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[coderabbitai]

Actionable comments posted: 2

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@src/lib.rs`:
- Around line 594-596: Several test cases call map.insert(...) and ignore its
#[must_use] return (a Key), causing clippy failures; update each call to either
capture the returned Key into a variable prefixed with _ (e.g., let _key =
map.insert(...);) or use the Key in assertions so the value is consumed. Search
for direct calls to map.insert in the tests (examples around the repeated
patterns inserting 1,2,3) and replace the bare calls with bound results (or
assert on them) to satisfy the must_use requirement.
- Around line 252-275: The bulk-removal paths (clear and drain) currently only
bump generations for slots where slot.take().is_some(), missing slots that are
"temporarily empty" (reserved via take()/scope()) so outstanding Key::restore()
can still succeed; update clear and Drain::drop (the drain implementation) to
treat any non-empty placeholder (i.e., any slot that is not the canonical Empty
variant) as a live slot that must have its generation bumped and be reclaimed:
iterate buffer entries and for each slot that is not Empty (including
reserved/placeholder states created by take()/scope()), increment
self.generations[index] (wrapping_add(1)), ensure the slot is set to Empty and
add its index to empty_slots so the map is truly emptied and Keys are
invalidated; apply the same logic to the drain() implementation and the
symmetric code block noted around the other range (the second occurrence) so
restore()/scope() can no longer resurrect values after clear()/drain().

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

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Run ID: 9f136536-5c97-4f62-a234-692b495692ba

📥 Commits

Reviewing files that changed from the base of the PR and between 083d106 and 1d25729.

⛔ Files ignored due to path filters (1)

• Cargo.lock is excluded by !**/*.lock

📒 Files selected for processing (2)

• Cargo.toml
• src/lib.rs