fix push "false" blocking replace in hx-location and hx-replace-url

[rameel]

Description

v2.0.11 regressed the documented HX-Location combination of disabling push and using replace:

HX-Location: {"path":"/test2", "push":"false", "replace":"true"}

The request and swap succeed, but history is not updated at all. The same happens with attributes:

<div hx-push-url="false" hx-replace-url="true">...</div>

Cause: #4093 (fix for #3966) removed the if (pushUrl === 'false') pushUrl = null normalization added in #3741 and reintroduced a late path === 'false' guard. A truthy "false" wins over replace again, and the late guard then returns {}.

Fix in determineHistoryUpdates:

• 'false' and false are normalized to null for both push and replace before choosing between them, so a disabled push no longer blocks replace (restores fix hx-location to handle replace #3741).
• The boosted fallback is skipped when push is explicitly disabled (keeps hx-boost="true" and hx-push-url="false" not working for anchor URL in v2.0.10 #3966 fixed).
• The late path === 'false' guard is removed since it is no longer reachable.

push / replace	2.0.10	2.0.11	this PR
"false" / "true"	replace	nothing	replace
false / "true"	replace	replace	replace
hx-push-url="false" on boosted link	push	nothing	nothing

Side effect: etc.push/etc.replace now fall back to the inherited attributes with ?? instead of ||. A boolean false passed to htmx.ajax (or in HX-Location with an explicit source) now disables an inherited hx-push-url/hx-replace-url instead of being ignored. This matches how HX-Location already treats false (#3740) and how htmx 4 behaves.

Corresponding issue: #3966 (regression introduced by #4093)

Testing

There were no tests for push being disabled together with replace, which is why this regression went unnoticed. Added:

• test/attributes/hx-replace-url.js: hx-push-url="false" + hx-replace-url on a regular element and on a boosted link; boosted link with hx-replace-url="false" still pushes.
• test/core/headers.js: HX-Location with push as "false" and false plus replace; boosted source with push/replace disabled updates nothing.
• test/core/api.js: push: false / replace: false override inherited attributes.
• test/util/util.js: recordHistoryUpdates() helper that records htmx:pushedIntoHistory / htmx:replacedInHistory events, so tests can tell push from replace.

Checklist

• I have read the contribution guidelines
• I have targeted this PR against the correct branch (master for website changes, dev for
  source changes)
• This is either a bugfix, a documentation update, or a new feature that has been explicitly
  approved via an issue
• I ran the test suite locally (npm run test) and verified that it succeeded