fix: respect MAX_BODY_SIZE in /bytes and /stream-bytes endpoints

[derekmpage]

Fixes #228

Changes the /bytes and /stream-bytes endpoints to honor the MAX_BODY_SIZE configuration variable instead of using a hardcoded 100KB limit.

Changes:

• Modified handleBytes to be a method on *HTTPBin to access MaxBodySize
• Replaced hardcoded 100KB limit with h.MaxBodySize check
• Returns HTTP 400 with descriptive error when requested size exceeds limit
• Updated tests to expect 400 for oversized requests

Testing:

• All existing tests pass
• Manual testing verified with custom MAX_BODY_SIZE values

Test Honoring MAX_BODY_SIZE

$ curl -v http://localhost:18080/bytes/10485760 -o /tmp/bigfile 2>&1 | head -30
* Host localhost:18080 was resolved.
* IPv6: ::1
* IPv4: 127.0.0.1
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0*   Trying [::1]:18080...
* Connected to localhost (::1) port 18080
> GET /bytes/10485760 HTTP/1.1
> Host: localhost:18080
> User-Agent: curl/8.6.0
> Accept: */*
> 
< HTTP/1.1 200 OK
< Access-Control-Allow-Credentials: true
< Access-Control-Allow-Origin: *
< Content-Length: 10485760
< Content-Type: application/octet-stream
< Date: Wed, 07 Jan 2026 16:24:32 GMT
< 
{ [3902 bytes data]
100 10.0M  100 10.0M    0     0  79.3M      0 --:--:-- --:--:-- --:--:-- 80.0M
* Connection #0 to host localhost left intact

File larger then 100k -> honor MAX_BODY_SIZE

$ dpage@MA-DPAGE  ~/pgit/go-httpbin   main ± $ ls -lh /tmp/bigfile
-rw-r--r-- 1 dpage dpage 10M Jan  7 11:24 /tmp/bigfile

Test exceeding MAX_BODY_SIZE

$ curl -v http://localhost:18080/bytes/10485761 2>&1 | head -30
* Host localhost:18080 was resolved.
* IPv6: ::1
* IPv4: 127.0.0.1
 % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                Dload  Upload   Total   Spent    Left  Speed
 0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0*   Trying [::1]:18080...
* Connected to localhost (::1) port 18080
> GET /bytes/10485761 HTTP/1.1
> Host: localhost:18080
> User-Agent: curl/8.6.0
> Accept: */*
> 
< HTTP/1.1 400 Bad Request
< Access-Control-Allow-Credentials: true
< Access-Control-Allow-Origin: *
< Content-Type: application/json; charset=utf-8
< Date: Wed, 07 Jan 2026 16:24:39 GMT
< Content-Length: 122
< 
{ [122 bytes data]
100   122  100   122    0     0   161k      0 --:--:-- --:--:-- --:--:--  119k
* Connection #0 to host localhost left intact
{
 "status_code": 400,
 "error": "Bad Request",
 "detail": "invalid byte count: 10485761 not in range [1, 10485760]"
}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.13%. Comparing base (1b709cc) to head (9b54746).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #229   +/-   ##
=======================================
  Coverage   95.12%   95.13%           
=======================================
  Files          10       10           
  Lines        1827     1828    +1     
=======================================
+ Hits         1738     1739    +1     
  Misses         52       52           
  Partials       37       37           

Files with missing lines	Coverage Δ
httpbin/handlers.go	99.25% <100.00%> (+<0.01%)	⬆️

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[mccutchen]

Thanks for the contribution!