fix: url-decode path segments in route layer

[yaythomas]

Issue #, if available: #222

Description of changes:

dex-local-runner (WebRunner) returned 404 for every Get/State/History/Checkpoint/Stop call against an execution whose ARN contained a literal /, and silently returned an empty list for ListDurableExecutionsByFunction when the function name contained : or $. boto's rest-json serializer percent-encodes those characters in non-greedy URI labels (e.g. / → %2F, : → %3A, $ → %24), but the WebServer's route layer wasn't decoding the captured segment before using it as a store-lookup key.

This PR centralizes URL-decoding at the parser layer so every captured path segment inherits the behavior:

• src/.../web/routes.py — decode each segment in Route.from_string. raw_path is preserved as the original wire path for logging. Order matters: split on the literal / first so %2F-encoded slashes inside captured values stay inside their segment instead of acting as path separators. The three callback routes drop their now-redundant per-callsite unquote() calls (added in fix: decode callback id in routes #117 for the same bug shape).
• tests/web/routes_test.py — strengthen test_route_with_special_characters to assert both segments[N] and the named field are decoded, while raw_path keeps the wire form.
• tests/web/e2e/routes_arn_encoding_int_test.py (new) — drive a real boto3 Lambda client against a live WebServer for every affected operation, with values containing the characters boto percent-encodes. Closes the test-coverage gap that let the bug ship: no existing test ran realistic boto serialization through the route layer.

Affected runners

• WebRunner / dex-local-runner — fixed.
• DurableFunctionTestRunner (in-process) — unaffected; uses InMemoryServiceClient which ignores durable_execution_arn.
• DurableFunctionCloudTestRunner — unaffected; ARNs come from the real Lambda backend.

Verification

• hatch test — 1245 passed (1239 prior + 6 new regression tests).
• hatch fmt --check — clean.
• hatch run types:check — clean.
• Pre-fix sanity: stashing routes.py causes 7 tests (6 integration + the strengthened unit test) to fail with %XX-in-error or wire-form-inequality messages, confirming the regression coverage is real.

Closes #222.

Dependencies

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[yaythomas]

some local-runner tests I ran:

Unfixed (origin/main / shipped v1.2.0):

get_durable_execution FAIL: 404 Execution %2Finv-unfixed not found
get_durable_execution_state FAIL: 404 Execution %2Finv-unfixed not found
get_durable_execution_history FAIL: 404 Execution %2Finv-unfixed not found
stop_durable_execution FAIL: 404 Execution %2Finv-unfixed not found

Fixed (this PR):

get_durable_execution OK (Status=RUNNING, ARN echoes back)
get_durable_execution_state OK (returns Operations)
get_durable_execution_history OK (returns 1 event)
stop_durable_execution OK