[BUG] File source re-reads file indefinitely when using codec in non-tail mode #6934

Describe the bug
When using the file source with a codec configured and tail: false (default), the file is read repeatedly in an infinite loop instead of being read once and stopping.

To Reproduce
Steps to reproduce the behavior:

1. Create a simple input file (input.log):

2024-01-01 INFO line one
2024-01-01 INFO line two
2024-01-01 INFO line three

2. Create a pipeline configuration:

test-pipeline:
  source:
    file:
      path: "/path/to/input.log"
      record_type: "event"
      codec:
        newline:
  sink:
    - file:
        path: "/path/to/output.log"

3. Create data-prepper-config.yaml:

ssl: false

4. Run Data Prepper:

./bin/data-prepper /path/to/pipeline.yaml /path/to/data-prepper-config.yaml

5. Wait 5-10 seconds and check the output file:

wc -l /path/to/output.log

Expected behavior
The output file should contain exactly 3 lines (one event per input line). Data Prepper should read the file once and stop processing.

Actual Behavior

The output file grows continuously, with the same 3 events being duplicated every ~500ms. The file source never stops re-reading.

Screenshots

Environment:

• OS: Amazon Linux 2
• Version: Data Prepper 2.16.0-SNAPSHOT (current main branch)

Additional context

• Affects all codecs (newline, json, etc.) when used with the file source in non-tail mode
• Not Affected: file source without a codec (uses legacy ClassicFileStrategy path — reads once correctly)

Root Cause
In FileReader.run(), when !tailMode && codec != null, the method calls readFileWithCodecOneShot() and returns early. However, lastRotationType is never updated from its initial value of RotationType.NO_ROTATION because the rotation check is below the early return.