fix(fs): return Generator from walkSync and expandGlobSync so iterator helpers are visible

[LeSingh1]

Fixes #7099.

walkSync and expandGlobSync are generator functions, so at runtime they already have iterator helpers (map, filter, take, drop, toArray, ...). Their declared return type IterableIterator<WalkEntry> hides those helpers from TypeScript and forces callers to wrap with Array.from(...) or write a manual loop just to use them.

From the issue:

const a = walkSync(".");
const b = a.map(v => v.name);
// Property 'map' does not exist on type 'IterableIterator<WalkEntry>'.

Narrowing the return type to Generator<WalkEntry> exposes the helpers. Generator extends IterableIterator so existing callers stay assignment-compatible:

walkSync(".").map((e) => e.name).toArray(); // now type-checks
expandGlobSync("*").map((e) => e.name).toArray(); // ditto

The async siblings (walk, expandGlob) are intentionally left as AsyncIterableIterator<WalkEntry>. The async iterator helpers aren't in the TypeScript lib that Deno currently ships, so claiming them on the return type would mislead callers into writing code that breaks at type-check time. Happy to change this if the right lib is on by default and I missed it.

Verification: ran fs/walk_test.ts + fs/expand_glob_test.ts with -A, 63 pass / 4 fail — the 4 failures (accepts skip option as regExps ×2, walks fifo files on unix ×2) reproduce on clean origin/main so they're pre-existing and unrelated.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.57%. Comparing base (cdf74a8) to head (a6756d0).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7166   +/-   ##
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  Coverage   94.57%   94.57%           
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  Files         636      636           
  Lines       52142    52142           
  Branches     9401     9401           
=======================================
  Hits        49315    49315           
  Misses       2249     2249           
  Partials      578      578           

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