docs: clarify parser timeout precision

[vibhor-aggr]

Summary

Closes #3798.

Documents the practical precision limits for HTTP/1.1 headersTimeout and bodyTimeout parser timeouts. Current behavior uses native timers for delays up to 1000ms and Undici's lower-overhead fast timers for larger delays, with a target resolution around 500ms, so these timeouts should not be treated as exact millisecond deadlines.

Changes

• Add the timeout precision note to Client options documentation.
• Add the same note to request-level Dispatcher options documentation.
• Mirror the guidance in the related TypeScript option comments.

Verification

PATH=/mnt/TBT_DATA/nipun/work/tasks/earn-100-legal/workspace/toolchains/node/node-v24.16.0-linux-x64/bin:$PATH npm run lint
PATH=/mnt/TBT_DATA/nipun/work/tasks/earn-100-legal/workspace/toolchains/node/node-v24.16.0-linux-x64/bin:$PATH ./node_modules/.bin/tsc ./types/*.d.ts --noEmit --typeRoots ./types
git diff --check

Results: lint passed, TypeScript declaration compilation passed, and diff check passed.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.45%. Comparing base (c7c7e7f) to head (79ae73c).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5543   +/-   ##
=======================================
  Coverage   93.45%   93.45%           
=======================================
  Files         110      110           
  Lines       37376    37376           
=======================================
+ Hits        34928    34930    +2     
+ Misses       2448     2446    -2     

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[mcollina]

lgtm