fix: validate H2CClient maxConcurrentStreams option

[trivikr]

This relates to...

Fixes: #5142

Rationale

H2CClient previously only applied maxConcurrentStreams when the value was valid.
Invalid user-provided values were replaced with the default instead of throwing like Client does.

Changes

Validate H2CClient maxConcurrentStreams values and throw InvalidArgumentError for invalid input.

Features

N/A

Bug Fixes

Validate H2CClient maxConcurrentStreams option

Breaking Changes and Deprecations

Should this be considered as a breaking change?
Although the types do not call it out, the value is expected to be a positive integer.

Status

• I have read and agreed to the Developer's Certificate of Origin
• Tested
• Benchmarked (optional)
• Documented
• Review ready
• In review
• Merge ready

Assisted-by: openai:gpt-5.5

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.21%. Comparing base (96fd5e9) to head (dc0c177).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5143   +/-   ##
=======================================
  Coverage   93.21%   93.21%           
=======================================
  Files         110      110           
  Lines       36247    36247           
=======================================
  Hits        33787    33787           
  Misses       2460     2460           

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