fix(api): avoid forced extrinsics index for broad/malformed time filters

[JSONbored]

Motivation

• Forcing idx_extrinsics_observed_order whenever from/to were present made broad or malformed time filters (malformed values were coerced to 0) cause D1/SQLite to scan-and-sort large retained windows before LIMIT, creating an unauthenticated query-amplification/availability risk.
• clampInt previously returned a default for non-finite inputs, which turned malformed bounds into a broad window start at epoch 0.
• The handler must ignore malformed bounds and only force the timestamp-leading index when the observed-at window is meaningfully narrow so the query planner can pick an order-aligned path for broad public requests.

Description

• Replace the previous coercion with a strict parseTimeBound that treats missing, empty, or non-finite from/to values as null in workers/request-handlers/entities.mjs.
• Only force the idx_extrinsics_observed_order hint when both fromMs and toMs are present and the window is narrow (toMs - fromMs <= DAY_MS), leaving broad/malformed filters planner-selected.
• Add regression tests in tests/request-handlers-entities.test.mjs to verify broad standalone time filters do not force the timestamp index and malformed time filters are ignored.

Testing

• Ran the focused unit tests with npm test -- --run tests/request-handlers-entities.test.mjs and all tests passed (128 passed).
• Ran formatting with npx prettier --check (and applied fixes), then ran npm run lint and npm run build, all of which succeeded.
• Ran npm run validate:api and the full npm run validate after the build and both completed successfully.

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Codex Task

[superagent-security]

Superagent didn't find any vulnerabilities or security issues in this PR.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.27%. Comparing base (796da14) to head (23d3e36).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2028   +/-   ##
=======================================
  Coverage   93.26%   93.27%           
=======================================
  Files          48       48           
  Lines        7755     7759    +4     
  Branches     2839     2840    +1     
=======================================
+ Hits         7233     7237    +4     
  Misses         92       92           
  Partials      430      430           

Files with missing lines	Coverage Δ
workers/request-handlers/entities.mjs	98.70% <100.00%> (+0.01%)	⬆️

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